Router did not work! Now being forced to pay for something that never worked.

I signed up for a supersonic account (fibre) last year around August (2024)in which I was given a “cooling off” period of 48 hours to report any issues with the device of which I did the day I received their router. The router was not working and never worked. I had back and forth calls with them and there was no resolution. I asked for them to come take their device and they did not. I later got a call from a manager stating that it was THEIR fault and THEIR router was faulty and were asking to give me a discount on my subscription and a new device! I said no and still asked them to come get their device. The device was only fetch this year (2025) in March! I am now being harassed with calls forcing me to pay for a service I did not use. Why and how is it possible for a person to pay for something they didn’t use even after they let the service provider know that their device isn’t working in the given time frame? I have honestly had the worst service with them and their call centres barely work, they do not respond to emails, they do not respond on WhatsApp either! I resorted to Facebook and still did not get helped! WHY AM I BEING FORCED TO PAY FOR SOMETHING THAT DID NOT WORK!? Even after I let the company know about their problem on their side!? I have emails and messages to prove that I did let them know and on time! I also know that they claim their calls are recorded so I am pretty sure they have all the conversations and times I have called them.