
The zero balance facility was linked to the fact that your employer held their accounts with the bank and, therefore, it was able to extend this facility to the employees. The facility ceases to exist when you are no longer an employee. Close the account if you do not need it or use it, or cannot maintain the required minimum balance.
You do not have any rights in this case because the facility offered to you was conditional upon your employment. Banks determine the minimum balance required based on their assessment of costs to keep and maintain an account and offer the facilities thereon. It is their business decision to fix this amount. You need to make your choice of the bank, based on your needs and abilities.;