How to change my address

I have been with virgin for 3 months with few issues since I first moved into my flat. The flats in my building are named and not numbered, however, and the only options online were to pick from numbered flats and I had no idea which one I was so I had to guess. Since then I have suspected that my flat actually may be a different number than the one I put, but my wifi still works so I figured there was no problem.

Today I received a call from virgin asking if I am moving because somebody else has signed up to virgin with the flat number I provided. I have a new neighbour who I am yet to meet so I assume this was them, but I think they have also got their flat number wrong.

On the phone call I tried to explain the situation but I'm not sure the employee understood why I was unsure of my flat number as he kept interrupting me. He told me to "confirm this information online" and that he'd call back later to make sure I had done it.

Is there any chance I misheard him and he was going to do it for me? I have looked at how to change my address with virgin but I can only do so if it's a mobile contract, a change of name or by telling them I'm moving (which I am not). I also do not wish to be charged a moving fee for this. I have no idea where to contact somebody about this so some advice would be appreciated.

In short: I'm supposed to change my address because of a mistake but don't know how and am unsure if an employee who called me will do it on my behalf