You should also call them, and don't say "I don't think you gave her the meds" as that will put them on the immediate defensive.

Say, "I brought my kitten to you x days ago, and you said you treated her for ear mites, but it has not worked and she is obviously still suffering. What did you give her, so I can write down the name of it, and how much?" All this can be accomplished over the phone. They may feel bad and say "Oh, bring her back in, and we won't charge you" or something, but in any case, you will want to have that info on hand in case the next vet asks.