All contracts and assurances made directly or indirectly for the loan or forbearance of money or other thing at a greater rate of interest than is permitted by law shall be void as to all interest provided for in any such contract or assurance, and the borrower or debtor may, in addition, recover from the original lender or creditor or other holder not in due course an amount equal to four times all interest agreed to be paid and in any event a minimum of $100. Every usurious contract and assurance shall be presumed to have been wilfully made by the lender or creditor, but a bona fide error, innocently made, which causes such contract or assurance to be usurious shall not constitute a violation of this section if the lender or creditor shall rectify the error within fifteen days after receiving notice thereof.