Been having this problem on and off for months. Open reach came and checked wires and it carried on. They came again and changed some connection from central area in bloxk of flats to mine.
It's hit and miss on both Ethernet n wireless. Even have powerline units to avoid wireless. Nothing changed in my flat but last 2 weeks been horrendous. Spend most of time using my iPhone for Internet.
Netflix is a constant buffer. If I'm on Ethernet and use wifi on phone to just tweet or open a page it's so so slow.
Changed channels. This is with one device wireless and one cable Ethernet.
I don't know what else to try. I cannot get fibre here.