Bajaj Finance — unnecessary bouncing charges applied every month

I have a personal loan going on with bajaj finserv. The emi should be deducted from my bank account automatically as i have done the ecs mandate for that. But the emi amount never gets deducted automatically, rather bajaj applies bouncing charge saying that there is insufficient balance in my bank account. That is not the case. I have sufficient balance available every month in my account. I have shared the bank account statement with bajaj. They have also checked the statement and agrees that there is sufficient balance available. But at the same time they are saying i have to pay the bouncing charge. I mean it makes no sense to me. This is contradicting here. And the bank statement is a concrete evidence. And they agrees to that. Still asking for the bouncing charge. There must be some internal issue at their end but no body is solving the issue. I have requested them many many times to help me out in this and to resolve the issue. But not getting any help or resolution. The issue still persists and i am getting irritated by their executive asking for the payment again and again and again.