Removing Samsung Pay should be the same as removing or hiding any other app. I never signed up for Samsung Pay (not willing to get a new card from a bsnk I don't like).
Setings > Phone/Applications > Application Manager >
Select the app and, in order, (1) delete the cache, (2) delete the user settings, and (3) delete the app. If the app cannot be removed, the option will be to revert to the original version: do so and then hide the app.
If you don't trust yourself then open the Samsung+ app. Select Support > Search Topics > Enter question or keyword = 'pay' > scroll to the bottom of the 25 results > tap on the "Can't find... > Contact Customer Support > choose phone or video.
HTH. YMMV.