No, this isn't "his new account": a quick check of his inworld profile shows that Nino Lassally has been a member since early 2007 and has payment info on file . Downgrading from Premium to Basic doesn't delete an account or any of the associated details (why would anyone assume that it did?), it merely changes the status of that account.
The details on file were obviously for a valid credit card (or the transaction would not have completed) so I really fail to see the problem. If the OP wanted the charge to go to a different credit card then he doesn't even have to bother fiddling with cashing out his Lindens - all he has to do is pay off that amount on credit card A (the one that he has on file) with credit card B (the one he wanted to use).
Simples <squeek>
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