Bandhan Bank — Charges led to negative balance on account

Address: Serampore, Mahesh , Hooghly, West Bengal

I am writing this on behalf of my uncle, who has two current accounts on Bandhan Bank Serampore, Hooghly, West Bengal. Today when we went to close the accounts, they told us both the accounts have due penalty charges which should be paid before closing them. I wish to know if Banks are allowed to charge penalties after it has turned NIL. A total of around 4000 is the fine ammount he has to pay. Please guide me with the right information about this matter, so we can take the required actions, Thank you.