I too am still waiting for my Mastercard from the Black Friday offer November 2015. I have gone through all the rigmarole required to log a claim, including looking for an order number that only existed in my previous provider's emails and have got no response - either to say I have or have not claimed correctly. I have also sent an email via customer services to BT and they too have not got back to me.
BT should not advertise such offers if they are not going to honour them.
If anyone can tell me any more about getting to the bottom of this I would be grateful.