Sorry to hear there's a problem, let's hope it's easily overcome.
I do actually have a tip for testing IR remotes, if you have a digital camera (or a phone with a camera)...
...With the camera switched on, point the remote at the camera's lens whilst looking at the camera's LCD viewfinder. Digital camera lenses usually 'see' the infra-red that's invisible to the eye, so the IR transmitter 'lights up' on the camera display.
In this case, if the channel up/down buttons are a bit flaky, it may be evident on the camera display?