Charged 99 more for data download without notifiying to the customer

I am using “ST_CR_MV_E_Connect_299” plan. with this plan, I can use internet up to 750 MB 3G data per month. for the month of July2014 to Aug2014, I consumed almost 500 MB data. but apart from regular billing, they billed me 99 Rs more for other downloads.
I spoke to Vodafone customer care about this, and they told me that, they charged this 99 Rs for other downloads on behalf of me.
here my questions are:
1) Why they have to pay 99 Rs on behalf of me. instead I can pay directly to that site using credit card or debit card.
2) while downloading, nowhere notified to the customer saying that this download is chargeable.
3) while taking this plan, they told me that I can use 750 MB 3G data. here as a customer, my intention is, I can Browse or download anything upto 750 MB which is allowed for download.