You would probably just have to /ignore him. When you say account details, do you mean minecraft details for bank account details?
Please provide screenshots of this happening. Action cannot be taken without proof. He most likley doesn't have your account information or know anything about you he's doing it to: A) Annoy you on the server B) To scam other players for money Best way to solve this is to /ignore the player or just ignore it in general. Also just show it doesn't bother you anymore and he'll stop.