Throttled at 20Mb

My 500Mb was running fine for two weeks. Usually measuring at 470Mb. Now it looks like it is capped at 20Mb. Anyone else being arbitrarily capped ? 

"Spoke" with customer support and they are either ill equipped to diagnose link issues or unwilling. After over 40  minutes and going nowhere slowly I gave up. The only coherent direction to the questions I could detect was  the desire to make sure the problem was inside the house. We've been through that one before in the last 18 years in the house and never has the problem been in the house or with my equipment, I'm not that stupid.

I see no alternative other than to go into the store and find a real human.

Any other ideas ?

Thx,

Steve A