It's not on is it? They reckon / know you ain't gonna bother for £3.69 and if you do, they'll argue the toss that the £8 admin fee stands, even though the whole thing was a cock-up of their own making.
Personally, just to be awkward, I'd argue the toss. And if I got no joy, I'd drag the Ombudsman in for good measure.
Thing is though, after all that, especially if I won my case, I'd be a marked man down the Sorting Office and literally everything posted to me from abroad would get the evil eye and I'd get slapped with every charge you can imagine.
Shouldn't be like that though, should it?