If they were paid, they were paid. So what's to be responsible for? Please re-submit the question, with more specifics, such as "my dr billed the no-fault company $100 and they only paid $90. Do I have to pay the difference?" (the answer to that is no BTW)
There is too little information in your question to give a responsible answer. Who is the '2nd party?' If it is an insurer, for example, they probably have a right of subrogation to a portion of the proceeds of any settlement or jury award. You really must consult a capable personal injury lawyer.
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