Loan cleared

Dear sir, L borrowed loan from CitiFinancial in 2011,repaid 12 instalments is Rs 3600.00 each, then after the threats started to me and I have proof of the SMS, sent by them CitiFinancial collection men. Later came to compromise and gave an proposal of loan closing @waiver of. Total of 50000.00. I paid too and got an letter from them as loan closed. Now Kotak Mahindra has taken over the CitiFinancial. They have sent me an notice to pay out standing of Rs 78000.00+.towards loan. If not filing of legal. I have received this from an advocate from pune. This is what happened. Please assist me. Thanks.