Tata Docomo — while calling to my tata docomo number call is getting all lines are busy call later.

If any caller calls to my tata docomo number it is that the caller is getting all the lines are busy and call again later. Tell me what action should one need to do to avoid that one.

I am not getting any calls, and even i am missing the important calls that are very much necessary for my education and job.
Please resolve this as soon as possible.