How to cancel O2 contract

I’ve got my PAC from O2 and I’ve bought a new SIM card with Lebara but before I install it and replace the O2 one what do I need to do with O2 about cancelling their contract? Or just swap the SIM and all will be clear?

Once you get the PAC code from O2 you have a month grace to find another carrier with that code,in this case Lebara. Activate Lebara SIM card, complete portin then your O2 contract won’t exist anymore. If you do it mid contract, ie you pay monthly, they’ll reimburse you any money owed as you pay monthly in advance. I did mine 4th February and was advised yesterday iI’ll receive a refund of £2.55p. Bottom line is active Lebara SIM card, do portin, once complete you’re free from O2 and will receive any money owed next time you were due to pay your O2 bill.

Many thanks