on 26-03-2020 16:43
on 26-03-2020 16:47
If it was an upgrade your old contract will just transfer to the new one.
If it's a new contracy and you want to keep your number, just call customer service to migrate your number Guide: How to find help & contact O2
If you don't want to keep your number, how to cancel old contract here Guide: Cancelling Your Contract