Consumer Redressal

I have purchased a flat in August 2011.With a down payment of almonst 50% of property value.On that day it was communicated to the builder that balance amount will be paid by bank loan.It was mutually agreed that after Oct.2012 if the don\'t give us possession he will pay us the rent.I applied for bank loan I got sanction but at the time of disbursement we came to know till there is no CC so we didn\'t registered the flat.As if the registration is more then a year old we can\'t apply for Home loan.Now the builder tell us that there was income tax raid and we have to pay 30% of tax of difference amount which is approximately 10 lac rupees ....Which is a big amount and why should we pay.....can any one help us what to do in this matter.