Take the battery off the phone whilst it turned on and then after a few minutes put the battery back again and hopefull the problem will be solved however if the problem still persists then u should take your phone to the S.E servise center and get it fixed!
go to gallery.mobile9.com and look for any apps that provide this feature and if u dont find any u can blocking unwanted numbers is that 1) go to contacts 2) creat a new group 3) add the unwanted caller to this group 4) go to general profiles in the settings menu. 5) choose the aleart for this...
These kind of problems are caused usually by viruses i'll suggest to get an antivirus for your fone from gallery.mobile9.com and run a full scan this will fix the problem.