Xfinity throttling my internet then denies it.

Okay so i wouldn't be stating this without having looked so very far into this. 

I have had technicians come out three times who all have some different excuse for why my internet is so slow when i pay for 1Gbps speeds. On 5 different speedtest sites I was showing consistent 200mbps, on xfinity's speedtest site i am showing 800mbps... I decided to then look a bit closer. When running a VPN on ANY speedtest site i show speeds of 600mbps+ on all devices. when i switch back seconds later off of a VPN i show back to <200mbps...So here is my question...

With knowing that there are laws that allow ISP's to throttle internet speeds as long as they are transparent about it, why lie, work in the shadows, and waste time and money bringing techs out for something that can't be fixed?

This is not network configuration either because i was able to convince the last tech to use a speedtest other than xfinity's service and we were able to see the same capped speeds. Please don't just delete this either because it would be very obvious that its happening at that point.