HIGH BIDDER GOT APPROVED BY HIS CREDIT UNION FOR AN AUTO LOAN OF $25K. CREDIT UNION HAD ALL DOCS FED EX'D TO US TO GET SIGNED AND NOTORIZED, WE DID. WE SOLD TRUCK TO HIGH BIDDER FOR $27K, WE STILL OWE $25K ON THE TRUCK IN WHICH THAT IS WHAT HE HAD TO GET A LOAN FOR TO PAY OFF OUR NOTE. 2 DAYS LATER NEW BUYER/HIGH BIDDER CAME TO PICK UP TRUCK GAVE US THE $2000 CASH OVER WHAT WE OWE ON IT WITH THE DOCS STATING THAT HIS CREDIT UNION WOULD BE FED'EXING THE PAYMENT TO GMAC, THAT HAS NOT BEEN DONE AS OF DATE AND ITS BEEN WELL OVER A WEEK, NOW THE NEW BUYER WILL NOT RETURN MY CALLS OR EMAILS AND WE STILL OWE GMAC, WHAT DO WE DO?