loan taken from market money lenders now asking for 5% interest

I have taken 5 lakh from local money lender . at the time of giving money he xfered 4 lakh in my account online and said to pay the same in 6 months with 5% interest , I thought this means 5% of total amount with interest till date i have paid him approx 4 lakh and he is asking for 5 lakh as base amount as rest amount got adjusted under the interest. I did not signed any document only did email conversations and that to no where mentioned 5% interest. What are the laws i can use to save my money now. pls suggest.