Hi,
Not certain this will work but go to your Contacts, select the number you want to block, tap the settings icon (either 3 dots or the right soft key below the screen and select "block incoming calls".
There are also various options described in this link which may also be of some help to you.
http://www.digitaltrends.com/mobile/how-to-block-phone-calls-on-your-android-smartphone/