Hi @asearle12 thanks for posting and welcome to our community.
I am sorry to hear you're thinking of leaving us. In support of the advice @DJ_Shadow1966 has given. If you cancelled your oomph package, even if you merely downgraded you would lose the benefits of oomph deal on your SIM. If you wished to retain a Virgin Mobile service on that SIM you would need to speak to our team on 789 or 0345 600 0789 from any other supplier, to change to some form of pay monthly deal, be that SIM Only or a split contract with a handset. If you did not take those steps then ultimately the SIM would deactivate and your number would be lost to you.
You also, when cancelling have the option to get a PAC enabling you to take your number to a new supplier. Again this would need to be actioned and used before any deactivation of your SIM.