Bharat Sanchar Nigam Limited - Didn t get the invoice of my connection

Last year on ** March I have taken the bsnl broadband connection that cost me **** one time payment after that I am getting the bill of every month that has been paid by me in the same month. But what about the **** for that I didn't receive any invoice. When ever I ask for they say we will give in some time but they never did. I am very my stressed due to this. There connection service is also very bad. Every month for more than ** days they connection is disconnected.