Hello markmaguire87
Thanks for taking the time to post in regards to your mobile account and tariff, we appreciate you raising this and welcome to the community.
Although there isn't a way to swap numbers between Virgin Media accounts we can look to see if the tariff can be changed on the numbers. From what you have said, during the set up process a new mobile account has been created as opposed to the Oomph tariff being applied to the existing number.
I'm going to send you a Private Message to look into this further for you and look forward to your reply.
Rob