i had 40+ lvl mage questsand i abandoned them. The npc doesnt have them anymore
Hi, Arminnius! o/
I assume you are talking about Classic, right? There are no known issues with class quests, and you should be able to pick them up again.
Usually, this issue of the NPC not having an abandoned quest again happens… when you check with the wrong NPC. That is, you get a quest from an NPC (let’s call him Charlie), and it sends you somewhere far away. You speak then with another NPC (let’s call him Bob), complete the first quest, and get a second one. Then, you abandon the second quest. Trying to remember where to pick it up again, you go and talk with Charlie, but he has no quests for you. After all, it was Bob who gave you the second one.
Hopefully this silly example makes sense. While I can’t say if it’s exactly what happened here, it’s what happens 90% of the time. So try and check pages like wowhead and ask some other mages around your level, I’m sure you’ll find the answer 
If you are absolutely sure this is a bug, you can write a ticket and they’ll have a look to verify if it is indeed the case, and try to help you, but keep in mind that unless it is really a bug, they won’t give you any hints.