How does the Apple TV connect to your network? If via wireless it may be worth just testing with a cable. Could be a throughput issue and the apple TV stream uses more bandwidth or the like.
Hi, Traffic levels look normal on the apple cache, have you tried multiple titles to confirm?
Also its worth then trying to stream to another device like a phone etc.
Its very unlikely your package would be downgraded from 30 to 20Mbps, and what is the VAT story about?
Cool Ideas offers what packages the fibre provider offers, pop your address into our site.