How to change contact number?

I have an appointment for DSL installation on 12.12, however the phone number in "Meine O2" is wrong, and I cannot change this. I have logged in to Meine O2 and selected "Login verwalten", then Haupt-Rufnummer, but this does not allow me to change the phone number or add a new phone number (see screen shot below, which only shows a number that I don't recognise and that I can't change). I need to change this number before 12.12 so the technician can contact me.
Please help!