Bajaj Finserv — unauthorized amount deducted from my account through ecs

Unauthorized amount deducted from my account through ecs. I contacted them on mail 8 times and they are simply replying that amount is not deducted by us and you may contact bank people. I contacted bank people and done investigation and bank people informed me that it is requested by bajaj finserv and they have only deducted amount from my bank account. Please help.