on 12-08-2018 12:00
i had the same issue at Waitrose o2 wifi, I accidentally, after being asked for my phone number misstyped my number...(probably old age!!!)
I tried all the 18.104.22.168. But this didn’t work for me, and i was unable to delete the wrong number, as i was advised i had been sent the sign in code...
I went to my O2 account and deleted the o2 wifi, associated to my phone. When i returned to the store, again it was showing the wrong number, but i was able to click send code again, and at this point was able to enter the correct number.
Once i got the code, all sorted and logged in ok.
So it appears, need only to delete wifi account, and then ask for a code to be sent again, and you can change the number.
Hope that helps. It was driving me batty.