HDFC Bank — negative balance (penalty charges without informing )

Address:

Mumbai City, Maharashtra, 400058

My salary account (In hdfc bank) was created in my first company, i left the company and joined somewhere else. Now my salary account in hdfc bank has been converted to savings account (Without informing me or warning me) in the month of october 2018 i had called customer care and raised a request to close my account as i did not want to use the account. I never logged in to my account through net banking and i did not use debit card. I have more than 5000 negative balance in my account. I request you to please take action against this bank.. Thay have no right to do whatever they want without informing the customer
And no one has informed me regarding the minimum balance n other things while opening the account.