Throttling

I have a telkom unlimited R599 wireless broadband system.Telkom states in the contract that users will not be throttled for streaming http and they encourage people to use their system for streaming.Every evening my connection drops from 30mbps to 2mbps due to throttling.This usually happens after 6pm.I only use the system to watch tv but after throttling makes it impossible to watch anything. I have phoned telkom call centres,but no one can ever give an answer to this. Telkom please explain to me why I am being throttled.