Outstanding showing on my closed credit card account by the credit card company

I have closed my credit card account in Nov 2020 however now Credit card company is claiming that someone has made the payment of Rs 50,000/- to my credit card account by mistake in the past before closing my credit card account in Nov 20 and now they have generated the outstanding statement of Rs 50,000/- on 20 May 2021 I also have the call recordings of them accepting that i have no outstanding on my card account while i was placing the request for closure of my card account through their call centre. However they are accepting that my account is closed but i have to pay the outstanding statement amount of Rs 50,000/- I have following questions regarding the above 1) What will happen if i default on this payment of Rs 50,000/- 2) Can they report this default to CIBIL and affect my credit score, since my credit card account is already closed in Nov 2020 and the same is also reflecting in my CIBIL Credit report generated through CRED APP? 3) Can there be any legal implication if i default on this payment of Rs 50,000/- 4) Isn't it the fault of credit card company that they have closed the account without settling my dues