Standard Chartered Bank - Harassment by bank even after the loan has been paid

I am a senior citizen and a retired person who took a loan of Rs.*,**,***/- vide the insta-loan account through my credit card towards the education of my children. The loan was promised at an interest rate of **.**% for a period of ** months.
Until March ****, within a period of ** months (as against the scheduled time of ** months), I have paid over Rs.**.**L (as against a total repayment of Rs.*,**,***). I have paid well over the scheduled amount payable and am no longer in a position to pay any further. I get threatening calls and messages from the bank and their agents to pay an additional Rs.*.**L, else I will face dire consequences.
I have been following up through emails and have also visited the branch in Pune to give me the rationale of paying an interest of Rs.**.*L on the principal of Rs.*.*L but have received none other than continued threats.
I solicit your intervention and urgent help in the above case.