Hey,
Thanks for reaching out to us!
Here is a helpful guide that will aid in stopping any unwanted emails from the payment processing https://docs.woothemes.com/document/unhookremove-woocommerce-emails/.
Also, the error you mention above would be generated by WooCommerce or a gateway add-on. Since we don’t handle any of the actual payment processing within our plugin it would be best to reach out on the WooCommerce support forums for help with that message.
I’m sorry I wasn’t able to give you direct answers here but hopefully this will help to get you pointed in the right direction.
Thanks!