File a formal complaint

In early December, we decided to cancel our previous internet service and sign up with Xfinity.  In addition, we opted to switch my cellular service to Xfinity as well with an upgraded phone.  Paid the initial fees and started the process.  The internet service was subpar.  Very spotty, sometimes not even getting signal sitting in the same room as the router.  Called it in and thy sent out a service rep to address the issue.  In the mean time, I will still waiting for the new phone to be shipped only to be told it won't ship until the home internet service ticket was closed.  Fast forward a week or so, the internet still hadn't improved so we decided to cancel.  Returned the router to the store and brought the new phone, still in the box to return it all and cancel service.  

They would not accept the phone in the store.  Said I had to call comcast mobile to initiate a return slip.  Did that twice both times being assured that the return slip would be emailed to me.  This has been at least two weeks.  Called again today to complain and once again try to return the phone.  Still in the box, never used.  I was told that my options were to stay with xfinity mobile or pay the price to outright buy the phone since it was past a certain amount of days.  This is completely unacceptable.  I tried doing this for over two weeks now.