As the title say, it does turn it off but won't turn it on.
I can control it on the smartthings app on my phone without any problems at all.
I have no Chromecast, if I get one will it work? Can it work without it?
My TV is a Samsung ue75mu6175
Could you clarify your current set up please to enable us to have a clearer picture of what you're trying to achieve?