Hi scampie,
Thank you for reaching out to us in our community and welcome, we are sorry to hear your Oomph Sim is no longer working and that you haven't received an O2 Sim, when you switch to a Volt deal your do get a Sim Via O2 however this is a totally separate contract and charge separate and in addition to the package price, this would also require a credit check, we are sorry if this wasn't done or advised.
What we generally do is generate a PAC code for the Sim with the Oomph then when requesting the O2 Sim we add this so the number comes straight over.
Regards
Paul.