Hi there, @RR1. Welcome to the Virgin Plus Community, and thanks for your post.
It's great to hear that you've already spoken to Tech Support, even if the results weren't an immediate fix like you may have hoped. When they said they were trying to fix it, did they provide any further clarity as to what the issue is? For example if it's a firmware issue or a local equipment issue (beyond your modem), it would indeed be more wide scale and they would not be able to provide an immediate solution.
Additionally, could you clarify as to what the Virtual Repair Tool actually told you when you tried running it? Does it tell you specifically the modem needs to be replaced? If you run it now, what does it say?
Otherwise when speaking to Tech Support, did you or they mention opening a ticket? Beyond your modem being replaced, this would be the appropriate next step for further investigation in most cases.
Looking forward to hearing back from you.