False Sale

I added xfinity mobile to my wifi because I was told they were running a promotion for free service for the first year, I would just have to say for the device in addition to $40 off of my wifi bill. They are now telling me a customer can't have two promotions. I would have never left AT&T to get a new phone if I was not told this. Where can I get directly to someone high up? Should I file with the FCC then pursue legal action? Help.