Product: Credit reporting

On XXXX XXXX, 2014 we took our dog to the XXXX XXXX XXXX in XXXX Oregon. We ended up having to transfer him to a different emergency clinic so we paid the bill in full only to find out later that they had lost the blood work and mishandled the case. After the lack of diagnosis and treatment all day at the XXXX XXXX he had to be euthanized. We expressed our dissatisfaction and requested they remove the charge but they only agreed to refund the lost blood work. We made it clear that we did not intend to pay because we felt that the service they provided was malpractice and if they insisted on billing us then we would have to pursue a complaint against them. When we received our credit card bill and only the lab test had been refunded we felt that the first step would be to dispute the charge with XXXX Bank rather than file a court suit. We filed the dispute on line immediately and received a call from XXXX who had a long conversation with us and felt we had a legitimate complaint about the quality of the service. They then sent the material to the merchant and gave them an opportunity to refute the complaint. They never filed a response which in the dispute process means the merchant accepts the reasons for non-payment. The merchant did not take the opportunity to prevent a chargeback or have an ongoing investigation. We received a card saying the dispute had been resolved in our favor and the charge removed. 
Months later we got a letter from XXXX XXXX saying that we owed this money to XXXX XXXX XXXX and I explained the situation to them. They requested a letter describing the events and the correspondence from the credit card company which we faxed to them with a request to contact us if they needed more information. They, however, entered it into their system as a dispute ( not resolved ) and never got back to us saying from their perspective there was a problem so we assumed that it had been handled. 
I received a week ago a notification from XXXX XXXX that there was activity with XXXX, Experian and XXXX to the effect we had failed to pay the bill. We had an excellent credit rating and for forty years we had never once received a credit report where all entries were not marked " paid as agreed. '' Yet despite this perfect payment record our score dropped XXXX points in a day to a " fair '' rating. We never ever received any communication or further billing from the XXXX XXXX XXXX so we assumed that the issue was resolved. I contacted XXXX XXXX who maintained we still owed the money and tried to scam us by saying we could pay off the bill and they would take care of it but with no guarantee they would follow through with the credit report agencies. Since we had paid in full at the time of the service and the dispute was then resolved in our favor the merchant should never have sent the bill to the debt collector and in in turn XXXX XXXX should never have taken it and pursued it especially after we provided them with all the information. 
I contacted XXXX XXXX who referred me to the person I had originally talked to who said that a computer program sent it on since we had n't paid and she had no idea it had been sent to to the credit reporting companies. When I called back they maintained we still owed the money and tried to scam us by saying we could pay off the bill and they would take care of it but with no guarantee they would follow through with the credit report agencies. Talks with supervisors got us no further. 
We disputed the negative report with the XXXX credit reporting agencies. XXXX are still in process and XXXX deleted the negative report. However, XXXX XXXX still has the " debt '' on their books and is charging interest ( according to credit reporting agency inquiries ) although they have never sent any written communication since.