Income tax on payment received under real estate 80:20 schem

Dear Experts,

I have bought a property under construction in 80:20 scheme (subvention ?). I have paid the builder 100% of the cost upfront, The builder credits interest (at home loan rate) for 80% of the cost into my SB account every month.

1. Is this amount received from the builder taxable? (As per my understanding, it is taxable under "Income from other sources" category). If the builder provides me with a letter that the amount credited is part of discount provided on the actual price, is it still taxable?

2. Where in ITR2 Schedule OS do I show this income? 

Thanks,

-SK