Offered 1 year of unlimited Xfinity mobile when I purchase Xfinity internet, however I am now being charged a monthly for mobile data

Hello, in January I moved to Washington DC and set up internet with Xfinity. The Xfinity representative on the phone offered me 1 year of an unlimited Xfinity mobile plan if I switched. I agreed, but now I have been charged $63.19 for the unlimited mobile plan, with a balance accumulating for the next cycle. I am very upset because I would not have switched to Xfinity mobile without being offered the promotion when I signed up for internet. 

Please assist and thank you for your attention to this issue.