Was I hacked so easy?

I was finishing the setup on my new IPad and after adding my credit card to my apple wallet I received an email that my credit card company suspected fraudulent activity to the tune of about $600 ( 3 pending charges and 1 they flagged and did not process) This was within minutes of adding my card! My Ipad is an open box deal from Best Buy (which is starting to make me think it wasn't as clean as they told me it was) and all I have is maybe 4 games and Facebook on it that I got from the app store. I only connect thru a secure wifi router so its not like I'm being careless 😟 I changed every password for not only my apple id and such but my email passwords and sign-ins for Facebook. How could my credit card have been hacked so quickly? The charges seemed to be from 4 different people. I'm at a loss.