How can I have my dental bill reduced/waived?

I recently had all four of my wisdom teeth removed. 3 of them were erupted which cost $160 each and the 4th one was not erupted which basically means it had to be removed with additional process and that tooth cost $300. so anyway at the time of the surgery we paid $254 (which the dental assistant had said that is an estimate since the insurance process takes upto 4 weeks) then a few weeks later after everything was done we received another bill witha balance of $89. Long story short, I do not want to pay this bill since we already paid $254. I spoke to them about my issue and she said she would speak to the manager who then said that they could not reduce the bill because they are contracted with the insurance company (no idea what that means) and that if they remove the balance it will be bad (she said it in a more professional way). So I want to know if there is anyway for me to get this $89 waived? I am a student and my parents work at a retail store so money is limited. Any suggestions?
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CALL AND ARRANGE WITH THE OFFICE TO PAY THE REST IN EQUAL AMOUNTS IN TIME
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