Did you know that someone was stalking me online?
Why was someone stalking you online?
I took something from them and they were angry with me.
Well, regardless of your theft what they're doing is wrong.  Stalking people, either online or offline, is not acceptable.  If it continues I'd contact the authorities.
I'm afraid of what they'll do to me if I report them.
Even though you're afraid, you still need to call the authorities. They are the only ones that can help you deal with your stalker the appropriate way and keep you safe.