Airtel — did not give promised extra offer

Address:

Mekkalil paipra, Ernakulam, Kerala, 686673

Recharge with Rs 399(all india free cal + 1.4gb data/day + 100 sms /day for 84 days).Apart from this they also offered 10Gb extra data to me.However i didnt get 10gb extra data even till the end of my offer period(84days).Raising this issue to cusomer care they said; you will get 10 gb only if you recharge again within 7 days after your end of data pack period ( after 84 days ) .This clause they did not mentioned when i purchase this product & they didnt give any indication about this extra 10gb till the end of my offer.How they can foolish their customer.please solve this issue immediately and instruct to Artel to provide sufficient compensation to me and warn penal action if they repeated same thing in future