As per the National Automated Clearing House Association (NACHA), there are only three allowable reasons to dispute an ACH Direct Debit charge as a customer:
The transaction was never authorised or the authorisation was revoked.
The transaction was processed on a date earlier than authorised (any date after is acceptable).
The transaction is for an amount different than was authorised.
Unlike credit card disputes, all ACH Direct Debit disputes are final and there is no process to appeal. If a customer successfully disputes a payment, you must work with them directly to resolve the situation.