@Silee0519 did you try a different HDMI cable, did you try settings the box to output "Other" instead of dolby digital in the settings menu.
Is the 4k box connected directly to the TV, or does it go through a AVR? I have a 4K Rogers box with a Samsung KS8000 no issues at all.
I have the KS9000 and had similar issues with the TV not working with 4K sources. After a month-long and very painful battle with Samsung and their horrific service department they sent me a replacement One Connect box. I have not had any issues with the 4K connections. I bought the TV as soon as it came out last year. The new One Connect box has a much younger serial number so I'm guessing they did some small tweaks within the newer ones.
I just bought this tv 65ks8500 that has this issue. Talked to a bunch of people Rogers tech, sales and no one knew this. Tried 4 different 4k pvrs from Rogers with this issue with no difference. Tried Roku Premier Plus, Google Cast 4K, a Sony Blu-ray 4K player that all works with sound. The search on google was "Rogers 4K no sound" that came up with this topic at the top. Now I know what the issue is. A Samsung technician will be visiting.
Update: got the one connect replaced serial number ending 63J2G1698 and now it works but get this the tv registers the 4k channels as 1080 at 60hz. If I unplug from one port to another the screen comes up as 1080 at 60hz. This is using the 4K PVR. My xbox360 connects at 1080 at 60hz also. The 4K channels do come clearer tho; compared sn1 371 and 997
Update: If I switch source in the menu from xbox360 to Rogers it says 4k in the banner. 3840x2160 at 60hz. So all I can say it works as it should