Mtnl dolphin
Network problem

I am using dolphin for last 4-5 years. presently shifted to kolshet, thane for the last one year. getting tower of hiranandani thane but it is not constant. hardly i can talk 1min before it gets disconnected. also some time showing no tower and roaming (cellone maharashtra). please do need in respect of network in kolshet, thane area.