There seems to be good help by knowledgeable people (including staff / engineers) on the Virgin message boards.
Not trying to duck the issue, but I do not have Virgin at my current address (had it for best part of 20 years previously), so would be unable to test / replicate any issues you might...
Your problem is wi-fi - so try a different router. Borrow one from a friend if you can, or read reviews on which routers work best with your provider if you can't borrow a different brand / model.