Cancelling Mastercard Debit that was issued as refund

That's not how they do it. Sorry. And we're customers, not employees. You'll need to call DirecTV (number below) to discuss this. 

I do not understand the issue other than you do not like how you were refunded your money.  In my opinion, you should be happy that you even got your refund at all.  There are so many people that do not get their money refunded to them and your complaining about how you were refunded is really petty. Use the card it is like a debit/credit card you can use it anywhere that takes Mastercard.