Airtel — unable to send sms to special numbers

I have tried to reach airtel customer for so many times and every time I get a different response from each one of the CSR.
The issue here is that I am not able to generate send SMS to 1900. Each time I am getting ' Error 69 Message not sent'
First time: When I called the CC @ 121 they told me that you have to clear the outstanding amount, I did the I send the SMS, nothing worked.
Second time: they asked me to pay some amount in advance, I did, nothing worked.
Third time: they asked me to. pay entire bill amount for the next month '600 rupees' and again I did, nothing worked out.
4th time: they raised a complaint and said that it will get resolved within 24 hours, I waited, tried again, nothing worked again.
5th time: they said to wait for 24 more hours, I did, and guess what nothing worked out again. It has been more than 48 hours and I didn't get any response neither my issue is resolved.

The issue is not only with the Port. I even can send SMS to a special number. For example 567678