This is so weird, I'm not exactly sure how to look into this. How are Virgin and BT generally considered in terms of customer service or lack thereof?
Virgin from my experience are pretty good, although the guy who deals with our local area is always available to fix stuff quickly and knows what he's doing, which might be atypical for the country as a whole. They seem pretty good though.
BT I'm not sure about from experience, but apparently they had the
highest number of complaints to Ofcom in 2016, so who knows? Their weird history as a former public company may affect that, especially as everyone sorta-kinda needs to have a BT landline for a phone, regardless of who they get their phone services from.
I tried doing an nslookup through both their DNS servers, but they seem unavailable for people not on their network, so it's hard to verify exactly what's going on