Ive used mineral oil in treating ear mites....just a few drops in each ear...then rub the ears so it gets in there good....some times ear mites cause ear infections..if this happens...use 1 part distaled water with 1 white vinegar...and use it as a ear wash. do this a couple times a day. If that dont work go see your vet again.
here is a link you might be interested reading
HowStuffWorks "Home Remedies for Cats With Ear Mites"