Why O2 is acting as a scam company?

I moved to my own apartment on 2024, but I had to move out soon because the owner was selling the apartment. I called to O2 to request a modification of my contract since I only needed the mobile contract. I was told that it was done on January 10, I even received email confirmation and everything to acknowledge this change. That's when the problems started. I've called and been told so many different ways to cancel my residential internet, I only needed proof that I moved to a new place and it was done. It has NEVER been cancelled, O2 even let me make the process to return Wifi, and NOW they are telling me that cancelling is not an option? 6 months later, charging me for a service I'm NOT being provided and today they tell me I'm not able to cancel. Now my question is, why did the first customer service representative told me it was possible? Why was I able to return the equipment? Why did NO ONE offered to see if I could have the internet installed in my new home? I demand a refund of my money and immediate cancellation of the residential internet. I've provided all necessary evidence. My next step is to find a way to sue this company. 

Edit o2_Antje: Moved from o2 Home to English Community