How does PAC transfer/ final billing work when you cancel monthly mobile contract?

Hi

I took out a first 24 month O2 contract on Black Friday 2017 (only ever had PAYG before hence my confusion). My contracted is now ended and I have still been paying the rolling monthly fee the past couple of months.


My next bill (for 24th Nov 2019 - 24th Dec 2019) for £30 will be taken by DD tomorrow. I rang 02 today and asked to cancel my contract as I think you have to give 30 days notice.

I asked for a PAC number as I want to change to GiffGaff. I asked if there was some way it would be confirmed that my contract is cancelled and was told that it only happens when you transfer the PAC to the new provider.

So what will I be billed for? Do I wait to transfer the PAC until 23rd Feb or do I do it straight away? Am I having to pay the full month or am I going to get 2 further bills if I do that? Is my call today the 30 days notice or is It when I transfer the PAC?

I'm just confused how it works and what I will be paying for and when is the best time to port the PAC to GiffGaff so that I'm not paying double.

Thanks