I've changed my direct debit details last month, and before doing so I've made a manual payment for the current bill. The problem, is that they've charged me again at the usual date via direct debit, so I've ended up paying twice.
I've tried opening a complain but didn't get an answer.
I've tried calling them, but they ask for letters of my password, so I've provided those of my account, but I think they expect some special security password, which I don't know how to get.
Any idea how I can get a refund for this?