DBS chola mutual fund
Change of bank details

I had sent a request to DBS to change my bank details for ECS. Now they are saying that they can see that bank details has been changed on second week of sept but still they are deducting from my old account instead the new one. But in my old accont their is not sufficient money so transaction failed and they had taken 200 Rs for two trans. They confirmed that they will not refund the money.

Please advise...