Visa Gift Card promised to me

I purchased a Samsung phone back in January of this year, when there was a promotion for a $400 gift card. I received an email that told me that I had satisfied the requirements for the gift card and that it had been mailed. When I didn't receive it, I checked the website, and it said that it had been returned. This had happened once before because Xfinity had left off my apartment number, so I called and requested a call back. When that call back never happened, I called abut 3 more times, only to be hung up on, with no call back. I then sent no fewer than 3 messages online for a call back, or even just to request that the card be mailed again, only this time to include my apartment number. I have heard NOTHING, and the status of the gift card still says "Returned". 

I have done agent chats 3 times, been told to call the same phone number that keeps hanging up on me, I was given a ticket #, and assured several times that I would "definitely" receive a call back or email within the next 4 days. I have once again heard NOTHING.

I sincerely do not appreciate these bait and switch tactics. I just want what Xfinity PROMISED me. I fulfilled my end of the deal, they have yet to fulfill theirs. This is at the very least a breach of contract, and I need resolution ASAP, as this has been going on for MONTHS. Otherwise I will need to return both of my phones, and cancel my mobile service.