Connection dropping out all the time despite the tests being okay

[BabyBean]

My connection drops out all the time and constantly under 300mbs which is promised. 

The main issue is the connection dropping out constantly but Sky will not help. They only offer a paid booster package. Their online tester keeps saying out internet is fine but it is clearly not. I could post videos or screenshots of it being entirely different to what the test says. 

[Highlinder]

@BabyBean  black or white router from Sky?

[BabyBean]

It's a white router, they sent us out a new one but exactly the same issues.