I also had the same issue you had. I'm on AT&T and activated Samsung Pay the first day it launched. Everything worked great with my fingerprint and AmEx card.
When the update came out, it would prompt me to register a PIN, then it asked to verify my fingerprint, then went back to register PIN, an infinite loop. As you said, no way to get into the app to change settings, remove card, etc.
Anyway, I went into Application Manager and selected Samsung Pay and tapped Uninstall Updates. When I launched Samsung Pay again, it asked me to Install. After installing, it went through the whole startup sequence again.
This time when it asked if I wanted to verify with my Fingerprint, I said no. (NOTE: I did not remove my fingerprints). It then asked me to enter a PIN and confirm it. I was then able to add my card back in and validate it. Once that was complete, I went back into settings and re-enabled fingerprint validation.
So far everything seems to be working. Not sure if going through Application Manager helped or not. I had not tried anything previous either.
Well good luck.
Kiliman