Hi ​@Steven1971 

You don’t say what type of SIM, so:-

Physical SIM
Your phone should still work with the SIM from your previous network as that account will not close until iD Mobile contact them once you have redeemed your PAC code when the SIM from iD is inserted. If you need a SIM quickly then you can visit the nearest Currys store to pick one up.

ESIM
If a PAC code has been redeemed for an eSIM but the SIM is not received, it usually indicates a delay in the activation process. The eSIM should activate automatically after the PAC code is redeemed, but it can take up to 36 hours. If you haven't received any confirmation or the eSIM is not working after this time, you should contact the network provider for assistance. 

It may be worth contacting the Live Chat to get this sorted:-
https://www.idmobile.co.uk/help-and-support
Type ‘talk to a person’ in the dialogue box to connect with an adviser rather than going round in circles with the chatbot. Make sure you have time to connect as it may take a while for the chat to start and to get replies as the advisers usually handle a few conversations at a time.

Good luck x