I ordered two power backups for my computers online and my credit card was turned down. What?

Almost immediately after my attempting to use the card I had a phone call from my bank. Was I trying to use the card and did I try on 3/29 to charge something online from Britanica to the tune of $75.90?

I hardly use my credit cards unless it is to order something online. I used it a lot at Christmas and never had any problems.

That charge for $75.90 is not mine - I have the card in my wallet - now canceled.

How do they get my number - have any of you had problems lately?