I don't know if it's just the one I visit, or London, or England in general, but I have developed a fear of going to the post office because the workers are so rude! (I am sorry if you are an English postal worker, by the way - may you be one of the nice ones!)
For one thing, I can never hear them, but every time I say, "Sorry? What's that?" they roll their eyes

and lean forward and act like I'm an idiot American for not understanding them. It's partly the accent, but mostly the way they often mumble...
And the other thing is that they seem to expect me to know exactly what I'm doing. If I ask, "What do I write here?" or, "Where do I put this sticker?" they don't tell me exactly what to do, they just wave or mumble something and I'm left as confused as ever...
Does anyone else have trouble with this? Or any advice for me? LOL. There are only so many times you can say, "What did you say? I'm sorry!" before you lose it...
It's probably your accent. The English are pretty tolerant of accents if English is not your first language, but not if you're American or Canadian.