SBI applied Commercial interest rate for my home loan, as construction didn’t started (after 4 years) asking for difference in interest for previous 2 years.

Sequence :

1. Took Home loan from SBI Dec-2010
2. Gave declaration that will start construction in 2 years else they can apply commercial interest rate.

3. Dec – 2012 no action taken from SBI interest rate remained same.
4. Dec – 2014 Got letter saying as you didn’t start constitution we are increasing rate of Interest and XXX.XX amount will be debited as part of difference in interest (Dec-2012 to Dec-2014)
5. Jan-2015 Closed the SBI Home loan as interest rate was high.

My Question is can SBI raised interest for past period?? I kept quite for 2 years and woke up after that and collecting differential interest after 2 years?

Thanks