How did they access my credit card? stolen?

A few weeks back I applied for a debit card. I received a letter with pin #. Stated the card was on the way in a diifrent envelop. After a few days it never came in and I called the cc company. They stated they sent out the card and decided to send a replacement.days later the card comes in. Fast fowad weeks later and I have unauthorized purchase on my account!! After multiple calls and waiting on my reimbursment I'm still wondering how they had access to my pin info? Personal info?