annoying caller

[Mischief]

so I have this person that has an obsession with calling my cellphone.. when I pick up and say hello, they just hang up.. I've already yelled a bit when I first pick up, and I've sat there quiet when I pick up to try and hear any voices.. The thing they forgot to do is hide their number.. Does anyone know how to find out who a person is by their cell phone #? I already plan on calling them and fucking their minutes up by using my landline. Gotta love one flat rate for my land line.