I would try the TagInfo app from NXP to read the tag. It seems that older Samsung devices didn’t play nice with MIFARE Classic natively, so you need to use the appropriate app. You could also try updating the S5 to the latest firmware (System Update in Settings).
Are you trying to set up a DT product, or some other access control card? None of the DT tags are MIFARE Classic, AFAIK. What is it exactly that you’re trying to do?