Thanks, all, for your comments. Some really good thoughts here.

I will try some of the tips I've seen here.

00000 and 99999 don't work on my cards; glad that some people have got it to work. Perhaps they work for foreigners whose credit card companies do not store data in a field called "ZIP", so any data will work.

I have learned that the world is a big, complicated place, and when things don't go my way it's not necessarily because someone was out to get me. (Who knew?)