ProfessorZ, I've had issues with GCM in regards to shipping being charged twice...I contacted them and waited and waited, even sent pics of the receipts and envelopes and all I ever got was the "second level/second tier" mumbo jumbo. Once it was getting close to the deadline to file a complaint with PP, I did so. There were two separate shipments that had postage due. The first complaint, they paid right away after PP contacted them. The second one, GCM did not respond to PP, so I filed a formal complaint. Next thing I know they said they refunded my purchase...I was confused at first, there was no refund in my PayPal account...then I realized they put the money back on the Ebay GC's I used to purchase the GCM Target cards. The whole amount. Not just the shipping I was double charged for. THE WHOLE AMOUNT. Even though I had already used those cards and they were now churning around. I just wanted the 5ish bucks from shipping!
Another example of weirdness is that I ordered 3 $100 Target GC from them; on the same day I got TWO envelopes from GCM...one had 3 $100 cards that were empty. The other had 4 $100 cards, only 3 were active. I cannot explain any of it. However in the end I was made whole. I strongly suggest you just file the complaint; it sounds like you have been patient and courteous enough. But that's your hard earned/churned money and you paid for merchandise. Including UPS signature delivery. Don't wait any longer to start a claim.