Have Openreach messed up my phone line?

[#1]

Had FTTC installed on 04/04/13 and my phone is due to migrate to Plusnet on the 18th.  When the engineer was here he said that the line speed was slow and that something wasn't wired correctly (an extension installed by the previous occupants by BT I think).  He said that he had sorted it out, but now I have an intermittent fault whereby some dialed numbers do not work and I get the recorded message "this number cannot be recognized".  The extension that he went to investigate is not used and I have only two phones connected elsewhere in the house.  I bought a new phone and tried that plugged straight into the master socket without the other phone connected but I still have the same problem.  BT's online fault checker says that there is no fault with the line and would I like an engineer to visit at the cost of £99!  Well I don't think so, as it is amazing that this happened exactly when my fibre was installed.  I managed to talk to someone at BT's fault reporting centre (India) and they say that they are going to investigate further.  However, I was wondering if it is anything to do with the transfer to Plusnet on the 18th?  I have a horrible feeling that I am going to end up out of pocket here in order to get the fault resolved.

[#2]

Hi there,
It's probably worth calling up and reporting the fault, the line should still be with BT until the transfer takes place so they should be able to get it sorted for you. Hope it's working again soon!

[#3]

It shouldn't cost you anything to get the fault resolved. If you've tried more than one phone straight into the master socket, then it's obviously not your equipment. You could try removing the lower part of the faceplate only - ie. not the upper vDSL filter part - and plug the phone straight into the test socket that is behind that plate. If it all now works ok, refit the plate and if it stops working, there's a problem with the wiring or the way the engineer connected it backup.
Post back with the outcome.

[#4]

I have resolved the fault myself but cutting the cable to the unused extension and insulating the conductors.  I think the message to be learnt here is to not let the engineer leave until everything has been thoroughly checked to your own satisfaction.  However in my case I had left my mum in charge as I had to be at work.

[#5]

If that is the only extension, then if you remove the faceplate as mentioned above then double check all extension sockets are dead by plugging a phone in with a filter and you can then actually remove the wires from the IDC terminals on the back of the plate by pulling them out vertically. If you want to have extension phone sockets, you can (legally) wire up your own and connect to the back of that faceplate. If you want advice on what you'll need and how to do that post back.