If there was a mistake concerning the posting of a payment over the telephone for your auto loan payment, you need to call the company and explain what happened through one of its representatives.After you have explained what happened, you need to write the representative confirming what happened giving all information that you have on hand, specifically the faulty confirmation number. Keep a copy of the letter for future reference. In your telephone conversation, you need to see what can be done about the thirty (30) day past due mark on your credit due to the mistakeIf the creditor refuses to assist you in your endeavor, there are credit repair companies that could possibly assist you in eliminating the negative credit mark due to the late pay caused by inccorrect information placed when you made the payment over the telephone.Good luck.