Had something similar happen with indiegala. Had an account with them for years, then one day, could not purchase some games randomly. Hit up their support and got the answer “Oh, the purchase was denied because your account’s email address is detected as a temporary email address”… The email address I’ve been using on that account… for years… Is temporary.
There are several reserved names in Windows. This is for backwards compatibility with mostly DOS programs. On your desktop, try and create a folder named “con”, and Windows should flat-out refuse. (Same thing for “prn”, “aux” and “nul”)