Owed credit from a closed account

Since DTV no longer prorates the final bill why would you have a credit?

I froze my account then canceled my service after the expiration date of freezing the account. 

That doesn't rate any credits.

My closed account has a negative balance because they owe me money after I cancelled my service. However, they keep sending me statements with the credit balance owed, but they have not sent the check for the credit  balance.