In my experience of BT Openreach, who manage the cables, they are most unlikely to respond when you have a problem at those times. I would suggest that you get some visual evidence, with timing, so that when they deny the existence of a problem, you have visual proof.
Daughter has plusnet, and so far their responses have been timely. However, as ever with call centres, be prepared to HUACA if you get a moron on the line when you complain.