Check out https://fast.com from Netflix. It's a speed test based off of Netflix's servers, so it will tell you your bandwidth to Netflix at any given time.
Then complain to your ISP if that doesn't match your advertised speed.
Then complain to your ISP if that doesn't match your advertised speed.
FWIW, even if you don't complain, it will help Netflix gather data that they can use to complain on your behalf.
There is no way to complain, but if we had some open, trusted services similar to speedtest.net to publish the effective speed it would allow people to make informed choices when selecting an ISP.