Overcharged for XFinity Mobile

I was offered a free line for 1 year, and then was told by the rep at the Steamboat Springs store that they would add 1 more line for $30/mo. The reality is that I'm paying $65/mo. for this additional line, which is not a deal at all. And I cannot find any evidence of a Mobile account on my XFinity App or on the website, so I can't see an invoice or a breakdown of charges. I'm just getting charged every month for it. What do I do?