WiFi Performance issues

in the last few days I have been having some issues with slow internet speeds, so slow that I can stream Netflix or HBO with my firestick with out lots of pauses to buffer. yesterday I lost patients with it and called Comcast. they help me trace the issue to my wifi being the issue. I was on channel 5 and before last week that was working fine. Now I can only get 4-5Mbps if I do a speed test from a tablet but I get 30 on wired. they suggested to use channels 1, 6 or 11 as those are non overlapping with others. I agree with that, I did change to 11 but that has not made much improvement. It seems that in my area there are close houses, some mine included converted to apartments so there are a lot of wifi networks near me and several with in range according to the wifi analyzer app on my tablet using 1,6 and 11. seems to me some one has put up more wifi networks recently. so is there anything I can do to improve the performance of my 2.4ghz wireless? :confused::confused: