Unused phone line

I went to A Xfinity store over a year ago where they told me if I change my line to a local phone number it will reduce my bill $10. I canceled the line in the store and got a new line that day. but have still been being charged with the first line this whole time. I called up Xfinity support and spoke to a supervisor and they told me there's nothing they can do. They said because it was over 120 days there's nothing they can do. I then asked if I can at least get refunded for the last 120 days and he again said there's nothing they can do. I also asked if there was any amount I could at least get credited for for future payments and they again told me there's nothing they can do. This doesn't seem right. The fact that I have had Xfinity for nearly 3 years now it makes me feel like I am not a valued customer. The supervisor just kept asking if I had any other questions and was unwilling to try to do anything to help me out. And clearly just wanted to get off the phone with me. There was no email sent to me about any warning of being over 120 days. Only billing information that was sent over to me but never realized I was being charged for two lines. Again, I would like to reiterate that this line was not used at all and there was no remaining balance on any devices. Please if there's anything that you can do to help me out it would be greatly appreciated.