It seems I was too quick to pass favourable judgement on Virgin.
They are now denying all my latest claims, saying that TopCashBack was not the last referrer, when it most definitely was. I don't use any other referrers to get to Virgin Trains.
It would seem that Virgin Trains are now reduced to the level of blatantly lying to get out of paying legitimate claims.
I posted upthread about Virgin declining (through Quidco) the completely legitimate purchase I made for an intercity journey on a Virgin train, with no cards, Nectar points, Virgin airmiles or benefits of any sort. They'd initially tracked it, but then declined some days later - a now-familiar pattern. So I put in a claim immediately.
Quidco got in touch a couple of months later to say the claim had been declined. No reason. No grounds whatsoever for declining, in my view. I emailed Virgin Customer Services to complain and was promised a response. I'm still waiting.
So yes, it appears they've now simply decided not to pay out at all, despite being on the cashback sites.
Incidentally, there are now numerous reviews on Quidco all telling the same sorry story. The 'all reviews' thread - the one automatically displayed - is in date order starting with the oldest, when Virgin actually did what they promised...with the strange exception of just one single gushing 5* review from late 2016 which has now been placed at the top so it's the first one you see, followed by equally glowing raves for Virgin's speed and efficiency in paying cashback, (!) from 2013. Other 2016 reviews - not to mention 2017 ones - give a more realistic picture - but are not shown on the initial review screen. Funny, that.....