Used my credit to waive fees

DO NOT GO HERE!!!
I last visited Infinity Dental back in 2011. I only came back for this visit as I had a credit on my account that they refused to refund me. After being forgotten in the waiting room, they told me my portion of the visit would be waived (since I had been there before, they would have known what my deductible would be after insurance). They later sent me a statement, trying to say I owed money. That was taken care of. But since I had such a poor experience on both visits, I decided I wanted my credit back and I started going to a different dentist. They have since stopped returning my calls and messages. They sent me some paperwork showing that they used my credit to help waive my portion of the visit. How is that waiving it when they're using my money? I have been out this money since 2010. Ridiculous.