Product: Debt collection

I am disputing this based off unscrupulous and incompetent practices from both the Clinics billing department ( XXXX XXXX XXXX ) and the collection agency ( The Collection Connection ). Initially back in XXXX of XXXX I received a billing statement from the clinic saying that my insurance company ( XXXX XXXX XXXX XXXX ) had paid their full portion and that I owed XXXX dollars to the clinic ( I will attach this invoice ). Several months later I received another notice saying I owed around XXXX dollars. I called the billing department and was told the insurance refused to pay and I needed to pay that amount. When I called my insurance ( XXXX XXXX ), I was told that the clinic had submitted several invoices that were denied because the clinic had filed them untimely. When I spoke to clinic to let them know this, they became confrontational with me saying because they could not get ahold of me for appointments, they submitted them late and it was my fault. The billing person let me know they did not care what the insurance company said, and they would send me to a collection agency if I didnt pay it. I spoke to many specialists at my insurance company that told me the clinic was in the wrong and they would have written off my balance since I was not at fault. XXXX XXXX said they would call the clinic to let them know the denial was accurate and not to harass me any further regarding this balance. After some time ( XX/XX/XXXX ), I wanted to follow up on this situation because I didnt trust that the clinic would adhere to XXXX  judgement. I called the clinic and was told that my balance was sent to collections and to deal with the collection agency. When I spoke to the collection agency, they told me that the clinic told them that XXXX  had paid all their portions and the remaining balance that now was at XXXX dollars due to interest was what I was liable for. This was a new narrative that I hadnt heard before. Again, the clinic initially told me back in XXXX  of XXXX that XXXX denied the invoices and didnt pay. The collection agency let me know I could dispute it and they would review documents then make a determination after speaking to their client ( clinic ). It took me sometime to obtain documents but every time I spoke to XXXX  they stayed consistently reiterating to me that the claims and appeal ( appeal I filed and currently awaiting documentation on ) were denied because the clinic filed them untimely. That for the state of California the submission period is within 30 days and the clinic submitted them way past 90 days. Several specialists attempted to call the clinic to discuss why they were harassing me, but they could not reach the office. 
I spoke to another specialist that went over each claim with me and determined XXXX claims were denied based XXXX denial code for untimely filing and/or XXXX code for duplicate invoices. Due to the clinics mishandling of these claims, the specialist said my patient responsibility should have only been XXXX dollars at the most .This can be corroborated by viewing the Claims History Itemization report that I will attach ( page XXXX ). After reviewing this report and other documents the collection agency called me and said that their client had changed the story once again and admitted that the insurance company denied them due to untimely filing and that they ( client / collection agency ) and their client felt it was unfairly denied. The agency told me that they sided with their client and would be resume collections attempts with me. Collection agency told me I could submit a written dispute and they would send that to their client. At this point I understood that this agency would side with their client no matter what ( ignoring actual documents from the insurance agency ) I asked the agency what proof their client submitted to back their claims? Do they have proof of appeal? the gentleman remained silent. I said, your client has changed their story yet again and is now admitting that they got denied based off untimely filing and think the decision is unfair, gentleman remained silent. I then asked him to go forward a place it on my credit and I would dispute with a different agency because I did not trust him to be unbiased and this reviewing process with his agency wasted my time. I would have rather them just say he was going to side with their client from the beginning, just like I wish the clinic would have admitted they are upset with XXXX  so they are taking it out on me from the beginning. As the patient did what I was supposed to do which was provide active or valid insurance info to the clinic and I should not be liable because the clinic did not do their part by submitting the claims timely and/ or correctly. Still to this day I have not been presented with any documentation or records from either the clinic or agency that supports their argument.