OK I have heard this quite a few times on several forums.
Here is how you solve this:
Go to settings.
choose : Device
choose; Call
Choose: Call Rejection
Choose: Auto Reject Mode (turn it to off)
This will solve this problem, Sometimes this somehow or other manages to turn itself on for some odd reason, I don't know why. But after hours and hours of frustration I finally figured this out.
Hope this helps everyone as much as it did me.