Tata Docomo — port message not sending

Actually i am trying to send message for "port" when i am sending an SMS it always says "message not sent". On the other side i am getting all kind of message from my friends & others and i can send also but the problem i am facing that i can't send a message for the port.

I am trying it from last 6 months

I tried to call the customer care number but said that number is switched off