I have faced the same prob for approx 2 - 3 weeks - it got worse day by day. Finally, on Jun 1 - 2 it died completely. Now, almost unuseable during the day. Barely useable after say 5.30pm. Have made a complaint, lets see.
From Sion exchange ( 2407 ).
MTNL guy on the phone says "Prabhadevi mein kaam chaaloo hai, dekthe hai".