Volume control too high

Your TV will have volume controls for itself. It's very likely that the volume on the TV itself was increased considerably. You should have volume control buttons on the TV itself and if you can't find them, try the remote that came with the TV. The longer route would be to reset the Slimline remote and program it for your TV again. 

Alternatively, if your Samsung TV is anything like mine, I had to shut off the internal speakers on the TV when I connected a sound bar as the TV audio was ever so slightly out of sync with the sound bar. The easiest way to do that is to use the remote that came with the TV. The Slimline can't change those settings on the TV itself.