I have a 50Mbps connection connected to a 300Mbps N WiFi router. In Fedora Linux the place I am, this computer has a USB WiFi antenna capable of 150Mbps, most of the time I get 50% signal strength, at this signal strength, it shows connection speed at 27-50MBps but from the ISP I'm only getting around 4-6Mbps.
I complained about the slow speed and the technician of the ISP brought his laptop and phone and showed the result of the SpeedTest on his phone and laptop, and it was around 45Mbps. But the computer with Fedora Linux which is little bit far away I'm only getting 4-6Mbps. The technician said it is because of WiFi and signal strength, I think he was lying, if the WiFi signal's connection speed is above 10MBps a 50Mbps connection shouldn't be a problem. I think they don't have enough bandwidth and when they came, through Mac filtering or IP filtering, they increased the bandwidth for his devices to allow it to get close to the advertised speed.
Is my suspicion reasonable? How can I confront the ISP with this irritating chicanery?