I have an iPhone 4S through tmobile and I need to block a number

I can't pay te extra on my phone bill that tmobile offers and my ex is harassing me. I can't go to the authorities and I jut need to block his number how can I?

Well I have AT&T and how I block numbers is by simply going to my missed calls or anything that shows previous calls. Usually for me it shows the person I called, who called me, etc. And at the bottom of the screen is a button to block a caller. Usually I press that and choose their number and it blocks them.

I don't know how it works for you but try going to the part where you can see missed calls or calls u made and see if there's a way to block someone.