The radio will constantly skip between the available channels and will always try to pick the one that has the least disturbances.There is a way to manually set a certain channel and thereby disabling the automatic channel select function. My experience is that it is best left at the default (auto) setting. According to the message, your radio was set to custom channel and they simply set it back to default. The job took probably less than 10 seconds, I hope they are not charging you for significantly more than that.
I have no issues with range, but I think it is about your expectations. 1-2 km is usually no problems with clear LOS. 3 km is doable in certain conditions, but that is the max range for the video feed (it is extremely choppy, keeps coming and going and hardly usable for flying). Anything beyond that and the video gets lost. The control signal is still fine though.