Ordered new phone in last 60 days and second line was auto added without my consent

At the end of July, I tried to activate a phone I purchased from Walmart under the BYOP program. Unfortunately was told at the Xfinity store the phone was locked. I was offered the same phone at the Xfinity store. They told me originally they could give me the phone at no charge. Then this changed to it's only 24/ mo (was never given a reason why this could not be free). My credit card was charged 96 dollars in August when I was only expecting a $54 payment. In looking at the bill, saw I was being billed for 2 lines. I live with someone who also has Xfinity and currently is paying 24/mo for her phone. I went to the chat and asked the rep if there was a way to separate the two lines so her bill could be billed directly to her (we're roommates so we pay our own bills). She told me she couldn't do this and I could call customer service but they would not be able to either. What is needed to get the lines split so the bill can be split? Looking forward to get this resolved