First of all, don't panic.
Normally, the full amount should get refunded in case cash was not dispensed and partial amount should get refunded if lesser cash was dispensed into your account within 24 Hrs from the time of ATM transaction.
If the full or partial amount is not reversed to your account within 24 Hrs, please raise a service request by calling our 24x7 helpline. Once you raise a request, we will update you with the status within 7 working days.