Incoming call notifications not working - Phone state In my Android phone, Incoming calls notification is not working.Out going is working fine.

Actually Whenever I am calling my mobile from my friend's mobile, Its saying "line is busy".
If I visit call logs in my mobile, I can see My friend's number in the log. 
I was having this issue for past 4 days. 

Thankfully, I checked the logfile(log.txt which resides in phone memory somewhere. I guess its the log of the whole phone) of my phone. In that file I can see the following log message 5 times like below.

Phonestate: Incoming call notify is disabled
Phonestate: Incoming call notify is disabled
Phonestate: Incoming call notify is disabled
Phonestate: Incoming call notify is disabled
Phonestate: Incoming call notify is disabled


I guess,  I have to change this phone state, I dont know how to change that. Can u help me out?
I just changed my whole software in REDMI Authorised service center. 
I guess the update corrupted my Operating system.