HDFC Bank — HDFC Bank Negative balance in my account

My salary account (In hdfc bank) was created in my first company, so once I left the company and joined somewhere else i had to open another salary account. Now my salary account in hdfc bank has been converted to savings account (Without informing me or warning me) in the month of March 2018 I had called customer care and raised a request to close my account as I did not want to use the account and they did say that they will follow up with the request and close the account. After that I never logged in to my account through net banking and I haven't used debit card . I logged into my account for some reason on 7th December 2020 and i see that i have Rs -6219 in my account. I request you to please take action against this bank.. They have no right what so ever to do whatever they want without informing the customer