Please confirm the date you selected with the company sending the debit. Was it a future date or did you authorize a same day ACH payment? 

Same day payments can be  authorized by phone or website to pay a bill or to transfer funds. If you agree, the funds might be debited from your account the same day.

Heres an example:

If you have a bill due on the 15th of the month, the billing company might allow you to call or use its website on the morning of the 15th to make a same day payment. Later that day the transaction may clear your account.

If you were debited earlier than expected please contact the company directly, or contact RCU to dispute the transaction.