How do I register my pac code on my new phone to use my old number

[Hannah19]

I have just switched from three to o2. How do I get my old number back? I have a PAC code? 

[Cleoriff · Accepted solution]

Hi @Hannah19 

All info here

Before we can transfer your number, we'll need your PAC code. This is made up of three letters and six numbers. You can get this from your current provider and it will be valid for 30 days. 

You can give us your PAC code when you order your new O2 connection or at any time afterwards. Once you’ve given us your PAC code you’ll switch to our network within one working day (Monday-Friday, 9am-5pm, excluding bank holidays). If we receive your code after 5pm, you’ll switch within two working days. If you provide your PAC code at the weekend, you’ll switch on the following Tuesday.

If you want to switch to O2 at a later date, just contact us with your PAC code when you’re ready to switch. You can give us your PAC code online.Or call us on 202 free from your O2 phone, on 0344 809 0202 from any other phone, or visit an O2 store. PAC codes are only valid for 30 days, but if yours expires, don’t worry – you can always request a new one.

https://www.o2.co.uk/help/device-and-sim-support/how-to-keep-your-mobile-number