I had a similar experience last year, only that was my permanent credit card, not a one time use. Fortunately my bank acted promptly to stop the payment, but I had to sign some kind of affidavit to the bank stating that I have not made the unauthrized fraudulent charge of US$5,000 on some auto parts!
I had posted about this here,too, but at the time I couldn't be 100% sure if my cc number was stolen from Ruelala because I had purchased from other online stores,too, but the fraudulent charge happened shortly after I made a purchase on Ruelala, and the same thing happened to a friend of mine who had purchased from Ruelala during the same sale,too.
Maybe we should all write to Ruelala about it since it has happened to quite a few of us, and in the OP's case, the one time use credit card numbers really are solid proofs that the problem came from within Ruelala!