Idrk but this seems like something that would get me in trouble with the IRS

I posted this on Moronic Monday, but didn't get an answer, so here:

Issue #1: I somehow accidentally ordered a chair from Amazon to my old address, on the other side of the country. It also used my old debit card on which I had my account closed after moving about a month ago. After a return request on Amazon and a few emails between the seller and I, they recalled the package and gave me a full refund. The refund was given by putting the $79.99 in my gift card balance... which is a problem because it was never my money to begin with (yes, I am actually complaining about free money), and I don't know how it processed the payment. I have no idea what to do, but I'm 17 (graduated) and have yet to take a personal finance class so I'm not super familiar with all this crap.

Issue #2: As with the complication above, this involves my mom's old card that is no longer activated. My Google Play Music Unlimited subscription was, for a few years after the card was deactivated, paid for every month by that card. I don't know how, but the payment went through every time.

Conclusion: What's up with these closed accounts looking as if they have unlimited money? Everyone has had cards expire, but what happens to the checking account tied to the card or the bank account associated with a credit card?