I bought D2 and LOD in December 2016 and I lost the game keys. How can I get them back?
If you claimed the keys to your Blizzard account you should find them there.
If the keys are lost and you never added them to your Blizzard account, then like other items you might lose they are lost and irrecoverable.
Taking a quick look you have attached the keys to your Blizzard account, so you should be able to log in and go to your Games section then click on Diablo II and LoD to see the keys you need to install the game.