So, this didn't help me with Virgin Media in the past (though I did get it sorted by finding someone relatively senior and bothering them until they got it sorted), but it usually does, as you say.

In general, I don't allow companies messing me around to profit from it. Even if it takes longer than it is worth, I make a point of principle that I somehow get more back from them than I was cheated out of or they neglected to deliver. Usually this ends up costing them much more than just behaving reasonably in the first place. I find finding a way to do this cathartic. It isn;t always entirely legal though.

If more people did this, it wouldn't be worth companies messing people around.