judging by the number of posts currently on this forum from people whose mobile number is now "stuck" somewhere between Virgin Mobile and their new provider. It does seem that there is a genuine problem at the moment.
Hopefully it'll soon be resolved. Perhaps you will need to call customer services back (free on 789).
If you want to say thanks > click 'Kudos'. Answered your question? > click 'Mark as Helpful Answer' also.