I have a half stalker what should i do?

Imet this guy he's like 20 though and since he was new to my country I decided to be nice I gave him my email address and then later my mobile number so he could ask when he got stuck or didn't understand anything abut here. But now he is kind of crowding in and emailling me ALL THE TIME plus phoning me too although I've tried acting not interested it's getting slightly too needy. Should i be nice and say back off or just ignore him?