This sounds so dodgy in so many ways. I can’t imagine (but I’ll give you the benefit of the doubt) that Amex would advise you to spend $8,300 on an upgrade that they would later reverse with MR points. For you to upgrade with MR->EK points there would have had to have been award space. Is this proactively checked ex post? How does Amex account for the cost of the upgrade? What if you had been quoted $20,000? I think your only hope is to get a release of that phone call. I personally would have requested the agents name, and asked whether this call was being recorded, in fact I would have asked for supervisor approval, before forking over that much money.