Help for 77years old parents . Threatening by recovery goons.

Namaste ?. My father was a State Govt Employee and retired in 2004. My Father used SBI Credit Card of an amount of 18000 & which was limit of 25000 . He paid 4 months minimum amount due and later when he desired to pay full outstanding amount it was shown more than expected actual outstanding. He had Spoken with customer care and they reduced lil amount but he was unhappy and decided to withdraw the usage of card and informed bank people that he will pay only outstanding amount . After long discussion they suggested for settlement and settled it he paid the actual outstanding amount and took the settlement letter and the receipts. The whole story happened in 2004. After 2004, we received call today in 2020 by recovery goons and threatening him to pay the dues of 1lac 10 thousand. My father is 77 years old he underwent in to stress . The recovery agents threatening my father to pay the whole amount else, his whole monthly pension will not be received. I had spoken with them they told me am unauthorised to speak on this issue. I told them to issue legal notice and will approach court with our evidences along with evidence . Please guide us how to tackle them . Every point of time they're threatening us. My parents are 77years old . My father is unable to take this harrasment.