Xfinity Mobile won't fix my line.

Okay, so back in March of 2019 I got a BYOD sim for my iPhone. Although, my previous carrier told me I couldn't unlock my iPhone because of some reason. The carrier told me this after I ordered the sim card. I thought I could unlock the phone because I did research and I qualified for unlocking but when I went to unlock it, they didn't. Anyways, I have been getting charged for the fee, even though I haven't used the service. I have called Xfinity Mobile multiple times to help fix the issue and every time they tell me that they will fix the issue. I even went in-store and asked, but the representative didn't even look at his computer and called me dumb for selecting the unlimited line. I waited 20 minutes for a minute conversation. I'm not gonna lie I am getting really irritated. I like the service because I have an iPhone 11 through Xfinity Mobile, but I'm getting charged an additional 50$ for a service I don't even use. Please fix. If not, is there a way to take back the phone, I wouldn't even care about a refund. I am still in high school and I have other bills to pay or else I wouldn't care all that much.