It's an unfortunate fact that the separation between BT and Openreach (insisted upon by OFCOM) allows each to blame the other for faults in a BT customer's service.
BT is also pretty bad at passing on details of customer faults to Openreach and, since you can't talk to Openreach directly, BT is the only source of this information for them.
Having said that, when I had a fault on my line recently, I got visits (in turn of course because BT had to confirm no internal fault before they could call out Openreach) from competant and capable BT and Openreach technicians who ultimately fixed the problem.
A lot depends on the quality and patience of the individual technician, so probably the best strategy is to keep on complaining to BT, put up with multiple visits, and hope you ultimately get a BT or Openreach technician who knows what he is doing!
