Tata Docomo — outgoing sms, call not working

Hello, this is merin kumar. I am having a tata docomo prepaid sim card from around last 7 years. I am having issue with sending sms to any other numbers from almost last 3 months (As i feel may be this problem is older). When i am sending an sms it always says "message not sent". I tried to contact tata docomo care their direct complaint number (198 or 121 or etc) doesn't work. Although i tried to contact with them on their tollfree number [protected] and other (Get from google) they say that my 10 digit number is invalid. And i am having trouble due to not able to send sms. Please help. Thanks,
Name : merin kumar
Mail : [protected]@gmail.com