i tested the router plugged straight into the wall socket, but before there was a slight extension cable, made no difference, unplugged sky and phone too
Like that?

If you're having problems with your line, jumping ISP will not fix the problem.
Do a quiet line test also;
This is done by connecting a corded analogue phone and dialling 17070 opt 2.
This needs to be done in the test socket, this can be found behind the faceplate of the master socket.
Don't use an ADSL filter
If you don't have a test socket disconnect all other equipment from the line.
There should be no noise on the line, any pops, crackles, hiss or hum etc will need to be reported to BT or who you pay line rental to as a "vioce fault".
Make sure that it is not an issue with the phone or any other equipment connected to the line or BT OpenReach will charge around £130 for the call out.