Long post (sorry).
Tonight I managed to change my sim only plan from a 6gb to 15gb (actually a reduction of 2 quid, result).
Got a confirmation that my plan would change at my next refresh, all good so far.
Then something funny happened. I looked on my status line and it seemed I was roaming. So I went into my mobile network settings and it's changed to ee. So I re-registered on virgin.
Guess what, I'm now on Vodafone. I haven't got a 5g phone yet, but for me the 4g and 3g signal is much better than before. I'm gonna see if I have volte next.
For information my country/operator code is 234 15 at the moment.