You are a smart man. I'll repost what I posted yesterday--
I would think it would be more along the line of trading in a car with an altered VIN number. I think the OP should respond by sending a registered letter to the buyer offering to buy back the coin at 50 dollars a month interest free.
There are laws specific to altered VIN numbers as there are to altered coins. It's hard telling what the court would rule in this situation but the OP did get the benefit of the 2200 dollars and should try to be fair within his ability to do so.* - Gary Kemper
P.S. Judging by some of the responses here, I don't think some can deal with multiple issues and look out for the best interest of the OP.