Root Call Blocker Pro doesn't work on Samsung Galaxy S5 G900FD and most likely, it won't. I tried for weeks and finally gave up. I contacted the developer of Root Call Blocker Pro and he responded that the app is not guaranteed to work with Dual SIM devices and there is no support for Dual Sim Devices. Moreover, the developer is arrogant and unhelpful and thinks too high of himself.
Another app that works on Dual SIM devices including S5 DUOS SM-G900FD like charm on S5 is "Root Call Manager" and it's cheaper. You may try the free version before buying Pro. The app may need a little bit of tweaking for S5 Duos but eventually, I could make it work (works for blocking both calls and SMS on my rooted SM-G900FD). So far, I am satisfied and the developer is very responsive and friendly and responds within 1 day.