Promised a Gift card never received

Hi, I was promised by an online rep that if I switch over to Xfinity Mobile, I will receive a gift card to pay off my Verizon Phone. They said they will send a gift card for $499.00 and I used that pay off my final bill with Verizon! When I contacted customer service after having the service for a month, I was told I had to pay off my Verizon bill first before I can get the gift card. The online rep and the in store rep never explained it to me that way! I want my [Edited: "Language"] gift card to pay off my Verizon Bill. I will go to FCC and Reddit because Xfinity has these out sourced online reps conning and false promising customers, just to add a mobile line. I should have stayed with Verizon, this whole process of transferring over has been terrible. Please assist with this matter!