Mercedes Lease Pull ahead - Payments not Paid

Turned in MB lease 3 months prior to the end of the lease. I had excessive mileage that was put into the new lease. I had the payment due while at the dealer. I was told not to pay as it would be paid. I asked over and over that everything was covered or put into the new lease. I was assured everything was covered. I received a notice a month later there was a balance due. It was for mileage - the dealer assured me that they have covered it and it would be clear. I didn’t receive any additional information from MB and thought it was taken care of. I received a collection 6 months later for a far less amount. I forward to the dealer and asked if it was a scam. The said they would look into it and if there was a problem they would let me know. After a long debate and incorrect information(they claimed I skipped a payment) from the dealer - I contacted MBFS and they provided detail information. They paid only 2 out of the remaining 3 months. The money received for access mileage was used for the unpaid lease payment. So there was unpaid mileage. MBFS charged off the amount and now I have a charge off. The money isnt the problem but the charge off affected my credit. Any suggestions?