I've run a test on the line which hasn't detected a fault. Just to confirm, what speeds were you previously receiving? Are you also running the speed tests wired or wireless?
How many telephone sockets do you have? What other devices do you have connected in addition to your router?
Does your master socket have a Test Socket?
Have you tested with a different microfilter at the test socket?
Would it be possible to post a photo of your master socket when the router is connected at the test socket?