How to block a number in Sony Xperia J
Shockingly, you can't block calls with Xperia phones.


  Unfortunately it's not possible to do this without installing any 3rd party software. I know that Truecaller has this function if you want to use a 3rd party app.


Source: official Sony forum

You need to download 3rd party softwares that are mentioned earlier:

TrueCaller

Calls Blacklist