New Sim. I’ve not received my new handset, how long do I have to activate my new SIM card?

you can activate the sim card when you need, if auto-renew is on payments will continue to be taken, here is a guide to auto renew https://bit.ly/3HYgR1g 

Once you've been given a PAC, you have 30-days to use the PAC.

If you don't, the PAC expires and you'll need to request another PAC in order to transfer your number DannyFe_1855973.