Kotak Mahindra Bank — Call from collection agent even after paying the whole amount

As per the letter given by the kotak bank I had paid the settelment amount but due to some reasons i had paid lately and while paying the collection agent told that it is fine and will not give a cal but after two months a person is calling and tell me to pay 1500 as ratification amount to close the account.

I had told him that keep the letter ready I will pay the amount and collect the letter.

he denied of giving the first, I told him that i am going to come to the branch and pay it.

but he started talking rubbish

the phone number he is caling is[protected] and [protected]

attaching the screen shot of the chat, he deleted all his voice messages and also he say that he will do whatever he want