Claiming interest on loss on let-out property

Dear Sir,
I have purchased an apartment and I have let-out that property. I have taken a bank loan to purchase the property, however i have registered the property for 10 lacs, however i have taken bank loan for 30 lacs. I have let-out the property and I am claiming loss-on-letout property for the interest for the complete 30 lacs loan i have taken. Now the tax officer is not allowing me to take the benefit of the complete loan and is asking me to take the interest only for the registered value of 10 lacs.
What can i do in this situation, let me know what options i have. Was I aware of these things i would not have registered for a lesser value.

Thanks in advance