Policy Bazaar — account closure due to irrelevant charges

Address:

sector 45, policy bazaar, Gurgaon, Haryana, 122017

Hi, i got a salary account in hdfc 1 year back when i was working at that time. After that i changed company & they provided other bank account. The new company have using only hdfc salary accounts. But my hdfc exsisted old salary account showing -7000 balance.
The bank converts my salary account converted into savings account & charged monthly.. Now its 7000 negative balance. Without my permission how can the bank convert my salary account into savings account? Even they are not intimated verbally... According to rbi guidlines on savings account banks not charge even its negative balance.
I approach branch, they said come to the branch and close here.
Please so justice to me. 7000 is huge amount. What is the solution?
What is the action will take against this bank.