Can I request my bank to reverse an ACH debit from a merchant who failed to provide the service?

My understanding is No. You can request reversal of the transaction if you dispute the authorisation. Since an ACH transaction is like an Internet cheque, think of it as a physical cheque. If you give it away to a merchant and they cash the cheque and refuse to deliver your goods/services, then this is a matter you need to take up with the merchant.

The ACH transaction (or the bank) are not at fault here. The merchant is, you need to seek a reversal from them.