bill above the credit limit with out any information

&lt;p&gt;&lt;b&gt;Location/place&lt;/b&gt;: Mundra, gandhidham,Gujarat &lt;/p&gt;<p><b>Name of company/service</b>: Bharathi AirTel</p>Sir,my Name is prempv iam using airtel postpaid connection my credit limit is Rs 1000/- per month but at the december month my bill rises to Rs 7500/- above the credit limit with out any information, they inform me only after the amont reaches Rs 3000/- ,when i complaint these to the coustamer care yhey said you got discount buy nw they are not giving any discont and daily disturbing me. So i request you to give me a juctice.