Hello Tim,
I just verified the communication log of your website. You can also find it at https://www.mrezone.com/sellacious/index.php?option=com_sellacious&;view=mailqueue
analyzing it I found out that 2 emails are hitting one 2 different contexts on order payment that is
order_payment_failure.admin
order_payment_failure.self
and both landing to your email, that means from the account you are trying to order something is also admin account so two emails are being sent one to you as a buyer informing that your order payment failed and another to you as admin that an order payment failed on your website.
You can anytime configure which one to keep and which communication to shut down from your backend email template view.
Let us know if we can help you any further.
-Abhishek
Team sellacious