Use a digital camera or the camera app of a mobile phone to test your remote control.
To do this just point the remote at the camera (or phone), press, in your case, the volume or channel button and check if you if can "see" a flash at the front end of the remote when looking at the camera (or phone) display. The flash should cease when you release the button. If it doesn't then the button may be sticking and needs to be cleaned. Try another button which works OK to see the difference.
Here is a link that shows how to clean the remote control buttons.
Hopefully this is of some help.