secondary dental overpayment insurance question?

my former primary dental insurance has a set contract rate of $433 for a root canal and they paid 80% which leaves a balance of less than $90. the dental office submitted my Explanation of benefits to my secondary insurance (at that time, but is now currently my primary) and they paid over $500 on that claim. I notified my former primary and they said that they will be requesting a refund to me since the dental office received appr. $400 profit since they are not allowed to take more than the contracted service fee and are in violation of their contract. so when i get this money back from the endodontist should i give it back to my primary who was at the time my secondary or should i keep it for myself? i hope this wasn't too confusing. i have already notified my secondary who is now my primary of the overpayment but they don't care and has caused me to max out due to the overpayment.
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The dentist,as far as I can see, did not violate his contract by accepting the secondary's erroneous payment. Obviously, the insurance made an error.The dentist's office will (if their billing dept is up to snuff) contact the insurance that paid secondary (since they obviously paid incorrectly) and the secondary will request a refund, which the dentist will have to send once he gets the written request from the insurance co. Your dentist will not refund anything directly to you...
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