I do not know the details about your specific setup, but with what you describe below, it sounds like you would need to perform an approved PCI ASV scan and complete an SAQ form (if you process and store the credit card information on the website than it would most likely be SAQ D-ME).
You can find all the vendors that offer the scanning service in the link below.
https://www.pcisecuritystandards.org/assessors_and_solutions/approved_scanning_vendors
I bought from these guys http://www.clone-systems.com it’s inexpensive, easy to run, and they have a WP plugin here https://wordpress.org/plugins/clone-guard-security-scanning/
I am sure some of the other vendors have something similar, just look at the list for the option that suits you best.
