Bajaj Finserv — demanding a money even after paid outs tanging balance in may 2019

My name is yogesh tandel and i had used bajak rbl credit card from october 2018 to january 2019. I had paid my outstanding balance in may 2019. I also confirm with collection agent and collection manager that my card is closed, after 16 months 1 recovery agent of bajaj came at my home and told that i have a due of 12, 000. I didn't use card since january 2019 and i had paid all my due in may 2019.