Golbat doesn't evolve into Crobat at a certain level. You have to get him to like you. The best thing to do is to put Golbat at the front of your party, and give him the Soothe Bell. Mine evolved at level 63, but yours can evolve at any time. Also, recommended moves for Crobat are:

Poison Fang/Mean Look(depending on whether you have caught Latios)Sludge Bomb Fly and Air Cutter

Hope this helps!