Product: Debt collection

On XX/XX/XXXX I agreed to a payment plan for a XXXX  bill that was to be covered by health insurance with the XXXX XXXX and it and was pre approved, but the insurance company refused to pay based on a underlying marital law, and paid bills at a lower percentage I filed a Appeal and it was denied. So my out of pocket was in access of {$16000.00}, for which I paid everything, accept payment of a XXXX XXXX XXXX Bill for $ XXXX XXXX  turned it eventually over to collection Optimum Outcomes for which I agreed to pay {$200.00} a month and they stated I would have 36 months to pay in full. I submitted my credit card information and they auto withdrew monthly on the XX/XX/XXXX. During the repayment, I paid other bills directly to XXXX and paid them in full. In XX/XX/XXXX I was receiving statements showing overdue bills from XXXX which my records show I paid those referenced. I called and submitted my payment history and recap spread sheet showing I paid all items on statement. I was able to find a payment I paid to them XX/XX/XXXX, it was agreed what was to be posted and found they posted it incorrectly that created un-applied funds, again thought it was resolved, they stated they had computer billing program changes and had a hard time recovering the records, so asked for me to submit my records, for which I did and I heard nothing, until I received a collection bill from Optimum Outcomes for these same said bills, XX/XX/XXXX. A patient service representative from XXXX  contacted me and she was researching my account claim since I stated I paid it her name is XXXX XXXX. I explained to Optimum she was working on finding my payments, and I talked with XXXX at Optimum Outcomes who was not understanding or willing to understand and I said kept pushing on me that " I am denying I owe these invoices '' and all I wanted was to show I paid these invoices, finally he gave me a internet web address to send in my support documents, for which I did immediately, he also kept bringing up my other collection bill XXXX, this was in a re payment plan, and said it was a separate concern, I specifically stated, that bill was in agreed payment plan and these are 2 different issues. I specifically stated I was not objecting to the surgery bill Account # XXXX. This gentleman was less than professional or listening so I was frustrated. I followed up in XX/XX/XXXX if they received my documents via email, during my call rudely they said they never told me to send my support documents there. I was out of the area and said I would mail them in to show support that all the invoices where paid, understanding the we are not talking about XXXX. Today XX/XX/XXXX I received a collection from attorney for account XXXX {$4900.00}, which made no sense since I was in a agreed repayment plan. I called Optimum Outcomes and they would not explain anything to me, all they said it was for non payment. 
They had my credit card and have always charged my account the XXXX with out issue, 1 time a year ago I did get a new credit card and had to update my expiration date which I called and did that to keep current, never besides that one time have I had a issue with my card or did I miss any payments. I feel they clearly choose to not run my debit to push me into default therefore to have this sent to an attorney and threaten me with judgement, since I was upset with their consistent unwillingness to resolve or attempt to help resolve, I am fighting to keep my credit in good standing, but I pay my bills, and I have shown XXXX  they posted my payments incorrectly, but I have never denied this bill with Optimum Outcomes XXXX, and have paid this down significantly and feel their practices actions are unjustified and not compliant. I have also provide written proof their claims : Paid XXXX and Submitted I paid all invoices on : XXXX ; XXXX ; XXXX ; XXXX ; XXXX ; XXXX, written and mailed and email website. 
I do feel that I should not have to pay the majority of these bills from my case with XXXX and XXXX XXXX, but my credit is important and know acknowledge responsibility. 
I feel Optimum Outcomes breached this payment agreement by not running my payments creating default by retribution. This is a clear unfair credit practice.