So I called Swisscom again, and they said that they do not use the port I have described and said that different providers use different lines (which I cannot get my head around!). The previous residents had an account with Net+
They said that I should look for an old-style TV socket - which I am yet to be able to do, thanks to the copious numbers of boxes blocking each room.
Thank you for the helpful replies regarding converters. Though if Swisscom are telling me that there is a different supply line, then an adapter won’t help.
Unfortunately despite the availability of fibre in my commune, it’s not in my neighbourhood.
So my internet-less states continues!