Money owed please help

Hi ladies, so like almost 2 years ago I was seeing a therapist and also ended up seeing a psychiatrist. I had two jobs at the time so I had insurance coverage. They didn’t bill the insurances correctly though and several claims were denied. I contacted their outside billing company several times to inform them of this and nothing was done. I ultimately stopped going to this practice and still got bills. Even after cutting ties I still continued to contact the billing company and my insurance companies to inform them of the errors. I’m still getting bills to this day and just learned today that it’s been handed over to collections for an almost 700 dollar balance but I don’t dispute that I owe them money, just the amount. My insurances should be picking up the bill, not my fault it wasn’t billed correctly and I let several people know about this. What should be my next steps? Dispute on my credit report? Complain to my insurance companies? Although I quit my second job this year so I don’t have that insurance anymore. Complain to better business bureau? Attorney general? I feel like I should have some recourse. How much follow up is necessary?