I won! I won! I won!
After another round of emails with Ms Hovnová (see Gobsmacked below), I got bored. So I sent my next email not from my private email account, but from my work email, which clearly indicates that I am a lawyer. Oddly enough, the very next day I received an email from Ms Hovnová offering me a complete refund in the form of a credit, which is exactly what I had asked for in the first place.