Bank charged higher rate of inrest

We are having CC Account with south indian bank availing 3 crores CCOL limit. we are a long standing customer of branch since 2013. Our Account has been classified as Non Performing Asset (NPA) on [deleted]. we were unable to pay the interest for the period November 2018 to December 2019 in time, because of unfavorable market conditions and distressful economic conditions. Earlier we have paid all monthly interests in time since 2013. As per sanction letter our account rate of interest is 11.8%(Loan sanctioned in August 2018) In December 2019 we cleared all the long pending interest dues and we got regularized our Account. During NPA period, the banker has charged penal @2% for overdue interest and also for CCOL limit of Rs. 3 Crores. But we heard the banker has to charge penal interest for overdue interest only and not for CCOL limit during NPA period as per RBI guidelines. Since January 2020, we have been following up with the bank for interest reversal but they have not responded. They have collected extra around 9.5 lacs to regularize our account. In January 2020 they have charged interest for CCOL limit as 18% which is very high. They have renewed our limits in February 2020. Kindly help me in this case whether we have to give complaint to banking ombudsman or to proceed legally.