False Billing

I have 2 cell phones lines. One is kept in a drawer 95% of the time cause the phone is very rarely used. Xfinity billed me $165 for the line I do not even use.  After being hung up on, on hold for long periods of time, told me to bring phone in... they could not look up the issue in their system.... returned to the store the lead team member left that told me to return. I cannot connect to get information to show where and when the line was used!