AT&T Direct TV Refund via Northlane

I was sent a Mastercard from Northlane for a refund from DirecTV after being incorrectly charged for unreturned equipment.  I was unable to transfer the balance and have been unable to log back in since then.  Three emails to Northland over 5 days have not gotten responses and their customer service number has no option to get to a person.  This is beyond frustrating especially since the error was made by AT&T.  I do not understand why they could not have issued a credit to my credit card or sent me a check.  I see many comments online about this being a scam.  I expect better from AT&T.