Switched from 3 to 02 and now 3 people can't call me - says number not recognised

[donomar]

Hi guys, I was on 3 for about 4 years but they keps messing up bills etc and eventually got fed up and switched to o2. All the people I know on 3 can't seem to call me - it doesn't even ring it says number not recognised. However I can call them and it works fine. I've been on o2 for a few months now and this has been happening. My fiance is on 3 as well so it's a bit inconvenient. Any help ? 

[MI5]

@donomar 

You'll need to call customer service to check the port went through OK.
Numbers here Guide: Coronavirus Community Help and Support 
When it comes to the reason you are calling stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to someone.
Say "Upgrade", "Lost/Stolen" or "Fraud" if you have to, to get put through to someone.
8.00am is the best time to call if you can.