Xfinity Support for bad phone!!

I have been a customer for over 26 years and am SOOOOO frustrated and now extremely angry!!! I cancelled my cable with Xfinity as it has gotten too much and opted for keeping the WIFI with Xfinity. The CS rep suggested a new phone at $5 per month. It sounded like a good deal, so I went ahead with it. The phone arrived while I was out of the country for over 2 weeks. When I got home, I activated the phone, transferred all of the info and started to use it. Problems plagued it like: it took over 4 hours - 3 days to get text messages, calls that went to voicemail were never found, all of my APPS took at least a minute if not more to get into, etc. It has been a nightmare and I have had to continue to travel with a phone that did not work. Out of extreme frustration, I reactivated my old phone thru AT&T which works perfectly. The AT&T customer service rep even tried to get the Xfinity phone to work, but he had the same issues with it. I reset the phone to bring it into Xfinity. Today I went into an Xfinity shop with the bad phone to cancel it. The manager said "you should have come into the shop originally when I cut my cable and we could have given you a better phone" and "this is a cheap one". I stated that I should not have to go into a store to get better service than online customer service!!! He said I had 2 options: 1) to pay off the phone (THE PHONE THAT DOES NOT WORK!!!!!) or to continue the $5 per month fee for the phone (THE PHONE THAT DOES NOT WORK!!!) I then asked for a new phone as this one clearly is a lemon he refused!!! He tried the phone without the apps or anything and said "it works." I have already spent about 20 hours trying to get it to work!!! Why would I go thru more trouble to bring it in?? I honestly have never had such a bad customer experience!! Now, I want to return the lemon phone and stop the $5 per month. At this point I am feeling so frustrated and angry that ideally I would just cut off all Xfinity services!