intermittent disconnection

Hello everyone, I apologise if this becomes lengthy! For months now I've had various symptoms suggesting a fault on my FTTC connection. I'm with BT (UK). I'm 3 routers and 4 engineers in. Fault reappears each time. Nothing can be done without proof of a fault, so I'm trying to gather...

I keep having this problem with my Asus PCIe wifi card that keeps disconnecting me if I am downloading any large file(s) after maybe 5-10 minutes of downloading. However, this only happens when I am connected to the 5ghz network, and works fine on the 2.4ghz network, albeit slower. I updated all...