Missing $100 Amazon gift card, multiple phone call and store visit didn't resolve the issue.

Back in May, I was offered $100 Amazon gift card to upgrade by a phone call. The agent and her supervisor assured me to get the gift card within 24-48hrs. 2 weeks later. Nothing. I called again and a different agent told me to wait another 3 months. In the meantime, she offered I could upgrade to 5 year price guaranteed without the impact to the gift card promotion. I double confirmed that I would still get $100 Amazon gift card within 3 months and then I accepted the offer. Now 3 months later, still nothing. I called again, the agent first told me I should wait 3 months, then I reminded him that 3 months already passed, then he became impatient and changed the tone that I should to local Xfinity store to get the gift card. I drove to the store but the store staff told me that they didn't have Amazon gift card and they didn't handle online promotion. He did say his manager would open an investigation for me and I should get update within 24-48 hours. Now a week later, no email, no call and nothing!  AT&T has been promoting their new fiber service for a while, I would have to switch if Xfinity is unable to honor what they promised.