Well bugger me sideways. No, silly. Not literally.
After all that fannying around with the Halifax (see below), I did write back to them, arguing that indeed it was their mistake that meant I was needlessly paying £20 for a mortgage interest statement that arrived too late to be of use. I expected another 'we are not to blame - tough shit!' letter from them.
Imagine my surprise (go on - imagine it. I'll wait here for you. I'll have a fag. Take your time.) when this morning they wrote to me, noting my comments, and saying that 'because of your long-standing relationship with us' they were refunding me the £20.
Bloody hell - really didn't expect that. They add: 'I sincerely hope that we will have the opportunity in the future to restore your faith in us' (as opposed, I imagine, to having the opportunity in the past).
So, as my mate Will Shakespeare said, all's well that ends well.
Lesson learned? As with the Virgin Media business, it pays to complain. So go on - get complaining.