My question involves business law in the state of: PA

On March, 19 2014, a customer had purchased a vehicle from our dealership. Purchase was made by credit card. Both parties (seller and buyer) had agreed that the vehicle was sold as is. As of today, I had checked my bank statement and a huge chunk has been withdrawn. Called merchant and found out that the transaction on March, 19 2014 was disputed. Customer complained about problems with the vehicle. Never returned our vehicle. Still driving our vehicle for free. With a vehicle being sold as is and showing proof to the merchant with a letter/copy of all the documents can the merchant service reverse the decision? What proper way should we handle this matter? Thank you.