Xfinity Mobile not honoring their early upgrade plan.

So I started a mobile line cause it was an excellent deal. I signed up for the early upgrade. I didn't like my first phone so I exchanged it. They You're saying I upgraded it but it was an exchange. 

Not they wont honor the upgrade service I am paying for. I told them I just want to stop the service. But I can't return it cause the phone isn't listed. 

They said take it to a store but I tried already and the store won't take it. Can someone either help me get this service canceled or get them to hknkr my early upgrade I signed up for?