2.4ghz Out and YOU KNOW IT

About 2 mo. ago, sevice on 2.4ghz declined to about 10%, and goes in and out. Lan at 50%, 5ghz still great. Moderns switched twice, no change. Service persons appear to have no clue or even acknowledge problem. But changed my ssid and made matters worse. to my devices are old which they are not. IS COMCAST WORKING ON THIS PROBLEM? DOES ANYONE HAVE A SOLUTION