Looks like you should contact the sales team as they can help with that – message them on Social Media if that works best for you -on Facebook (https://o2uk.co/O2CFB) , Twitter (https://o2uk.co/O2CTW) or Instagram (https://o2uk.co/O2CIG)
Or you can call them on 0800 081 0255
It may be worth speaking to Virgin as they are the ones who send the information to o2 to process. You can contact Virgin on 0345 454 1111 or 150 from a Virgin Media Phone.
Sometimes SIMs are easily misplaced while in transit. But once they leave o2s warehouse, the journey of that SIM lays with the postal service unfortunately. You should be able to pick up a SIM for next to nothing in many stores or pop into an o2 store and they will handle everything for you.
Hope you get sorted, I know how important it is to have an active SIM and service.