deduction of balance

&lt;p&gt;&lt;b&gt;Location/place&lt;/b&gt;: jalandhar&lt;/p&gt;<p><b>Name of company/service</b>: tata docomo/gsm</p>i use tata docomo network on 26 may 2013 i use tata docomo 5rs internet pack i use it after using it i found they deducted my 66.41 rs after that i got my 17.71 back and got 8.43 mb back after calling to cost care tell me that bal. is deducted due to post usage and how is it possible if i have 8.43 mb data left