16-12-2018 22:13 - edited 16-12-2018 22:16
You need to contact customer services http://www.o2.co.uk/contactus and ask them to migrate your number for you.
You can also transfer any credit to your contract account and if you have any rewards saved, claim them first or you will lose them.
OnePlus 6 (O2 & Sfr), Z3 Tablet (Three UK), iPhone 8+ (EE)
on 16-12-2018 22:15