ST.MARY'S MOTORS 41/481 Rajaji Junction,Chittoor Road,Ernakulam Cochin 682035 Kerala — Delivery issues

I have booked one Royal Enfield standerd 350 on May 24th 2014 with 5000/rs booking charge.At that time they told me that the expected vehicle delevery time will be on 6th month of the day of booking and the price will be around 1.13 lakh. But they didnt inform me anything regarding the booking status till now and now i called them and they told me that the amount(around 5000/-) is increased. The increase of price mainly because from Jan 1 onwards, the tax rate increased by central govt. But from my case this month is the 8th month after booking the vehicle. My complaint is, they didnt delever my vehicle within 6 month and now they are telling the charge is increased.As a customer, what will i do.