OP, please post some proof that you sold him the account and I'll tag it.
I don't think he can sign a message, as I suspect he is personally selling an hacked account and the new buyer hacked it again!
Yeah, the account probably has changed hands at least one time in the past, either hack or bought and there is a post gap in his history before this sudden revival with the yobit campaign that is a bit suspicious.
But if there was an account sale for 60$ you'd have to wonder why the OP chose to sell the account and not use it himself for the yobit spam.
And the only explanation rises another obvious question.
OP, just how many accounts you have in stock
:P I gave him the info and the address keys.
And you have no copy of them whatsoever? Really?