Cancelling credit cards to cancel offers?

Any idea what would happen if I just canceled my credit card?

Let's say I sign up for Ancestry and decide to cancel. Yes I know you can call up, but is it possible just to remove your credit card number. With mine you can do it online. Would there be repercussions? Just curious, feedback appreciated.

Yeah, stupid move... it'd be probably sent to their bill collection agency, and if I'm not mistaken, it'd go on your credit report.

they will probably try to charge it and then since it will be rejected , they may try to contact you and if all not successful they will contact collection agencies