AT&T False Promises

I signed up for AT&T Fiber back in March and they told me if signed up I would receive a $300 reward card. This was my main reason for doing so since no other provider was offering that much. After getting transferred 5 times, and being on the phone for almost 2 hours everyone tells me that the promotion was not offered. The person who got me signed up lied to me. They still can't figure this out and no one is helping. Not a great start for a new customer.