How to block someone's number from calling you?

I'm with AT&T and have an iPhone 5. This guy that I don't know will not stop calling me and texting me about something I know nothing about I keep telling him he has the wrong number but he won't stop calling and texting. Is there anyway I can block this guys number?

I don't how haha

If you're not familiar on how to block a number on your mobile device, you can easily contact your telephone service provider to block the number for you within their database.

I've been into a similar situation before and and received a similar advice when I posted my complaint at http://www.callercenter.com. Well, the resolution worked so I'm sharing it with you.