We’re very sorry for the experience you've encountered so far with NOW TV on your Samsung device, however we do have an update that should resolve this issue.
Can you please check that you're on the correct firmware version for your TV, you’ll need to be on version 1147.
If this is not the case, you are able to download this version on to a USB and upload this to your TV. Version 1147 can be found via this link here: http://www.samsung.com/uk/support/model/UE75MU6100KXXU/
On this page there is a 'DOWNLOADS' section which should have version 1147 available. Click the download link and download to your computer.
You can chose to follow the steps below or open the manual below download section on the link above.
Copy the downloaded file to a USB stick.
Double click on the file on the USB stick to extract it.
Put the USB stick into the USB port on your tv.
Open the menu and navigate to Support/Software Update - do a software update and when it asks you if you would like to check your USB stick say yes.
This should pick up and install the new firmware.
If you have any further questions please feel free to let me know.