When some one calls me. The first attempt will say number is busy and then on second attempt the call goes through.  This works only if called right away the second time

This happens with everyone. 

That does not stop here. If they try to call after 10 mins, it will again say my phone is busy and then they disconnect and call again. 

Tried network reset. But it did not work. 

This very much annoying as someone would always get my number busy..