Double billed.

I have been struggling since October 2022 to get a issue resolved. I am being billed for 2 lines, altough I only have 1 line. If I try to terminate 1, and leave 1 active, they switch my internet off. I am not going to pay for two lines, physically there is only one line and one router. It sounds like a simple concept to grasp, why am I having so much trouble getting it resolved.