National Payments Corporation of India [NPCI] — Nach

I was investing in different mutual fund schemes through ECS mode. Recently, my banker has deducted a certain amount towards NACH charges. I urge the bank that since i was already investing through ECS hence there is no logic to deduct amount towards NACH charges. NACH charges should be implemented on new customers and not to the existing customers who are already enrolled in ECS. My banker has informed that NACH charges shall be applicable to each & every investors.
Kindly clarify whether bank can levy NACH charges to those investors who were already investing through ECS?