Buyout promotion not honored

I switched to Xfinity mobile services last August and have been trying to get the buyout promotion as promised since then.  The Xfinity rep who sold me the mobile package never mentioned that I needed to submit a phone bill from my old provider or that it would take 16 weeks to receive the gift card.  I have followed up periodically since August and have attempted to get the info they need once I found out they need the old bill, but this is very difficult once you have changed services, as I am sure Xfinity is aware.  Anyway, I still am unable to get the buyout gift card as promised and am very frustrated.  I have now gone to the store (again!) and was told they cannot assist.  Xfinity please stand behind your word and promotions and get this gift card issued as promised!