How can banks assist customers in cases of fraudulent debit transactions?

Depending on how the fraud was committed, a bank's ability to help or not is gauged by how much they feel they were involved in the incident. If your credentials were compromised and someone made a debit withdrawal, this is really not the bank's fault. They can certainly assist, once you have lodged a formal police report and have written to them in writing.

Banks don't shy away from such things, but they will try to put the blame on you most of the time (why would a bank want to implicate themselves?).

Always seek legal help and file a police report at the earliest.