I use hamstring but my target is still moving like i didn’t press anything.
My char is not being able to attack resulting in bad gameplay.
Why is this not fixed?
Hamstring is not a root or stun effect, it is only a slow - so they will keep on moving, if slowed down 
In PvP there are about a 100 things that remove, mitigate or ignore attempts to slow a player.
True but it is the only way to catch shamans in wolf form and druids who just shapeshift out of it so I wonder what’s the point of this ability being global cooldown if it’s not doing what it is supposed to to - slow the enemy so we can catch them ?
Maybe a buff is in order, so it could really be worth the global cooldown, right now rogue’s auto attacks are laughably way better that this global ability or just buff it to 70% or make it not global so it can be as good as the other abilities ?
EDIT: I find there are WAY TOO MANY TIMES I feel like I have to press the ability just to realize the debuff is already there but It does nothing.
Turn into a Ghost Wolf, increasing movement speed by [Winds of Al’Akir: 30 / 30]% and preventing movement speed from being reduced below 100%.
This makes you and the Shaman ‘equally’ as fast, if he isn’t slowing you. If you are wondering why a Shaman in Ghost Wolf is not slowed, no matter how many times you reapply hamstring - now you know.
This is the game, we got tools to slow, root, tether, stun, etc, to force combat. With charge and leap, you are and should be able to keep up with the shaman if you use your tools.
Concider this: The game would not be fun for the Shaman, in your example, if they could not get away at all. Warriors are sticky and got the tools to stick. These counter-tools are there to give the other player a chance to get away.
As you wanted a 70% slow:
Piercing Howl - Spell - World of Warcraft (wowhead.com)
This is the 70% warrior slow you are looking for. Heck, you even got the possibility to take a 70% slow on your Bladestorm if you so chose.
Don’t forget that warrior have hard CC too to stop any escapes in a kill window.
Overall, it to me do seem that you got some gaps in game-mechanical knowledge and how your foes classes work. Spend some time and learn how they work, then you will also learn the how’s, what’s and if’s, so you can catch them or know that they got away.
Most players find themselves hitting this wall when they reach around 2k-2.5k rating. Where your knowledge counts heavily in turning that 49% win matchup to a 51%.
Just play some more, invest some time into other classes and you should profit. Perhaps you will also get the other side PoV how frustrating it is to play Vs a sticky warrior.
Trust me, I played enough to know the pain of catching my prey - especially in 2s vs Surv/Rdruid… Still, that is what it is, part of the gamemode and the experience. So…
Never forget this though: Zug Zug !! When you are not having fun Zug Zug’ing, take a break for the day 
The shaman example seems to work only in 1v1 situation. In the arena there are often classes that just slow me way more and I am unable to catch the pillar circling healers.
Hell, even shamans have stuff to slow me down. It’s just not fun to play.
PvP is supposed to be fun, right ?
Warrior is already close to being too mobile and sticky, if they gave us more or removed others peel… well, they would have to re-balance warrior. I am talking removing the Mortalstrike effect or reducing our damage by 20-30% to make up for the new uptime and pressure.
My point was and still is, they are supposed to be able to get away by pillarkiting and that jazz. If they could not - well, then the game would be dead for them.
PvP is indeed supposed to be fun, sadly - you are too focused on your own minor inconveniences that you don’t consider what fixing those would do to the other side of the equation.
All melees have too much, except maybe DK. But that’s another topic, and yeah harmstring is not the best snare available, on the other hand you have 2 bladestorms for root immunity + rallying cry (with speed increase) under battlefield commander, 1 aoe snare and root (battlefield commander again), 2 charges, 1 heroic leap, 1/2 intervene for mobility, with addition of 1 fear (best one available), 2 stuns and a potential root if you select warbringer as pvp talent.
It’s more than enough to have fun as a warrior. If you want to focus on 2c arena, then be prepared to run behind a pillar for most of your games, that’s how 2c is played. If you want to have more fun, play 3c.
The times when my char is NOT SLOWED and the enemy char have hamstring applied but nothing is happening are way too much.
Shaman’s wolf with hamstring is faster than my char without any slow on them.
DKs with hamstring debuff are faster than my char.
Dragons use a thing where they have hamstring and my char can’t catch them at all even tho they should be slowed
Hell, even rogues’ slow is better than the GLOBAL COOLDOWN that is needed to use hamstring. Among other stuff to make the arena expirience feel awful.
No need to mention stuff like hand of freedom and other abilities that just make hamstring useless.
I see the debuffs and because I can’t believe devs really made it like that press hamstring again just to reaply it but can’t catch the enemy at all.
There is literall no button to press to counter the enemy while they are sprinting around the pillar probably laughing their whatever off the warrior class designer.
I agree that other classes need abilities to counter the slows provided by the good class designers but warrior’s class desgner slow is just … well bad design.
Come on warrior class designer! I believe in you! Don’t let other class desginer laugh at your slow design for warrior being useless! I know us forum guys can give you 999 solutions if you ask but I am not sure that our opinion will not be … balanced 
And if the warrior class designer thinks that hamstring is ok while so many classes just ignore it … maybe we need another class designer to pay our money to ?