How to block calls from iPhone?

Hai, well about a few weeks ago my brothers had signed up for this stupid thing on some social site called weeworld for something called gold points and they put my number in, now I keep getting calls and calls about picking up a kit for something, and I'm scared to tell them it is a mistake because they record the convostation and they'll report me to the police, how do I block the number for iPhone 4S?
Or should I just tell them it's a misunderstanding?

Why would they report you to the police? Just tell them it's a mistake.

You need a block tool to manage it. Http://www.seeblockednumber.com

Here is how to block incoming calls for your iphone: http://www.digitaltrends.com/mobile/how-to-block-calls-on-an-apple-iphone/
Besides, you can also use an app like Mobile Nanny to help you block specific phone numbers: http://www.mobile-parental-control.com/