[anigbrowl]

The retailer is not much wiser than you, all they do is enter the number to find out whether it's valid or not. Talk to your bank/card issuer, by calling the phone number printed on the back. They deal with this sort of thing all the time, and will probably straighten it out very quickly. If you run into difficulties, find a solicitor; investigating it yourself is likely to be a monumental waste of your time.

[kindly]

It has nothing to do with my bank card. It was only the use of my email for some account. I had no account on X before this point. I imagine if they used my bank card they would use another email for the account on X and not inform me of what they have done.

I already checked with my bank to make sure no money has come out. That was the first thing I did.

[anigbrowl]

Then why did your title say 'credit card fraud'? Where does the credit card come into the story?

[kindly]

I said "potential credit card fraud". Sorry for the confusion. The potential fraud is not being done to me. I just wanted to know what I should do if I suspected it.

[anigbrowl]

OK, that makes more sense. I guess it's hard to fully explain a situation in an Ask HN post.