Xfinity Store mishandled my trade in and now it’s lost and still on my account.

I talked with someone at xfinity about the trade in value of my iPhone SE. I was told I would get a $150 check. So I took it to the xfinity partner branded store located at 1900 Street, Sacramento CA. The person that took it from me never made me fill out the Asurrent   Paper work. She never even took the phone off of my account. Now I’m being told there is nothing they can do about it even though I clearly says on their computer who helped me trade it in. I would gladly take the money credited to my account. But they just want to tell me That they can’t find it and that I’m out of luck. It’s still on my account. [edited for violating forum guidelines]