GIFT50 Code Not Applied at Checkout

I was emailed a promo code "GIFT50" to use at checkout upon purchasing an internet plan. I did so within the qualifying dates, but was unable to apply a code at checkout. Several representatives have told me I would be eligible upon activation of my plan, but others have told me I was supposed to use the code at checkout (which wasn't possible). I feel lied to and as though such a promotion doesn't actually exist, scamming customers to sign up with Xfinity. I would like this code to be applied to my order.