Well, sudden changes in behavior had to be caused by "something". If you didn't change your Zen Cart site settings or software, then ... it must be either your webserver, or the webserver's mailserver, and/or your email service.
One such possibility could be:
Maybe your hosting company changed their mailserver's spam filters? Sometimes mailserver spam filters don't like the short emails with ALL CAPS in the subject and just a short line of numbers in the body of the message. That's why more recent versions of Zen Cart contain an explanatory message about what the extra-digits email is for ... mainly to satisfy mailservers that the content is reasonably legitimate.
As to the CC digits you've lost ... they're lost. You'll have to contact your customer for that information.
I'll add that this sort of thing is just one more reason why a live gateway is a good idea.
I'll also add a plug for upgrading. The Zen Cart version you're using is officially no longer supported. And, as I mentioned, some adjustments were made in newer versions to attempt to avoid the symptoms you are reporting. I realize that doesn't "solve" your immediate problem, but putting a plan in place for an upgrade would be advisable.
In the meantime, ask your hosting company about what (so-called) "improvements" they've made to their servers lately, especially related to mail and spam filtering. If your email is on the same server, then those problems are all on the same box. If your email account where those messages are configured to arrive are on a different server, maybe that server has changed some spam/filter settings.
You might even try configuring the module to send those emails to a different mail account.
