Brighter Dental, P.C.

I recently received a bill showing an outstanding balance after I had already paid the amount I was quoted. Something is fishy.
Before my dentist apt I was given a break down of what my dental ins would cover and what I would be expected to pay out of pocket. On the date of services rendered I paid my part of the bill ($240) A few weeks later I received a statement with a note that said "my dental insurance allowed more $ than what they charged". I called to ask about it and the dentist's office explained that they billed my ins $586 and my ins allowed $602. I don't understand why I have a remaining balance if my ins allowed enough to cover it. The dentist said they had to raise their fees to compensate and that was why they were seeking an additional $131.60 from me. It doesn't sound right to me and I don't appreciate them taking advantage of me. Who else are they raising fees on and taking advantage of? I did contact my dental ins and they said everything was covered and resolved.