Virgin's overcharging was absolutely not "mistaken". It was quite clearly deliberate. I had no option but to move house, and my new location was unserved by Virgin. I repeatedly challenged the size of the in-contract ETC they were claiming when I arranged termination over the phone, but as life was far too busy (like having a 96-year old father to arrange care for, move house, etc., etc.) I didn't have time to take it further with a formal complaint.
6 months later I received a cheque for over £100. Don't tell me they weren't deliberately trying to fleece me, when I quite clearly challenged their calculations.
After hearing this response from VM, I'm even less likely to use their services in the future. Not that they'll ever serve the deeply rural spot I'm now in....