Bizarre phone fault - can anyone shed more light t...

Question

We have recently moved into a rented house and switched to BT from day one as there was a special offer phone/broadband/TV package. But we have an odd phone fault and wondered if anyone had experienced similar?
We have a main socket which is different from any shown on BT website, with two identical slots each labelled "BT exchange line", each with a sticker with a different number (does not seem to be a phone number): the socket looks a few years old and the stickers have an obsolete customer service phone number on them. 
We can plug a phone into one of the slots and it works and we have also now plugged the BT hub into the same slot via a splitter - that also works. The other slot is dead, so we assume it might be two separate phone lines.
But the main socket is in our daughter's bedroom so we need to use the various extensions in the house - we also need to connect our BT hub near the TV.
When we plug a phone into any of the extensions we get a dialling tone and can dial but when we get to the eighth digit (always the eighth) of whatever number we try we get "the number you have dialled has not been recognised".
After going through the BT faults site (no use as our main socket is not shown there and there is no reference to a similar fault with the extensions) we rang BT and got the call centre, which was frankly no help. They did not recognise this fault and seemed to have no technical knowledge at all. I asked to speak to an engineer and was told (I quote) "this facility is not offered" - this is clearly unsatisfactory (in fact, utterly stupid), our previous phone company always had experts on the end of the line if necessary and they twice helped us to sort out problems in a few minutes with no need for call out.
But BT said, very unhelpfully, that the only way they could help would be if, rather than a two minute phone chat, we called out an engineer for which we would be charged £129.99 if the fault turned out to be beyond the master socket. We had no way of knowing whether this was the case in advance (neither could the call centre operative enlighten us), given  that the extensions DO seem to be connected to the line (as we have dialling tones), just not working for reasons that may or may not be to do with the main phone line or the way BT has connected our number. 
Obviously £129.99 is a ridiculous call out charge for what could be two minutes work. It also seemed suprising that BT could not immediately access a record of what sockets were installed by BT itself in the house and that the call centre seemed never to have encountered before the type of socket we have. And that BT then advised us "to contact a local engineer" - should not BT have local engineers, we live near Reading so hardly the back of beyond?
In fact, even more bizarrely, a BT engineer, local or not, had already visited WITHOUT an appointment a few days previously after we had first contacted BT to say the phones were not working properly and phoned us from outside asking for access to the house....but this was during a period when we had notified BT in three separate ways (phone, text and e-mail) that we would be away.....
All in all we are mystified by the nature of the fault - if anyone on this forum has experienced similar, it would be great to hear about it - and equally so by BT's response to it and by its apparent policy that no-one with any expertise should speak to us about it without a £129.99 charge - hardly the way to welcome and retain new customers in what is now a competitive market! After a forceful complaint it seems that we will now be able to talk to someone other than the call centre....but not clear whether this will be a qualified engineer and getting this far has already taken hours of our time.

Answer 1

Sounds like you have a LJU4.... In the early to late 90's when people got dial up BB a lot of them took a second line, so they could use phone/internet at the same time......
To stop people requiring two overhead cables from the pole and two different NTE's BT created the Drop Wire 10b, a 2 pair aerial cable. Orange/White pair 1 and Green/Black pair 2. They then did the double socket, LJU4 so you wouldn't need 2 separate sockets....
I would imagine the LJU4 would be your *Master Socket* and the others would just be extensions off it.... That's just my opinion though, without actually seeing the wiring setup I couldn't say....
Can you get a pic of the socket and a pic of the wiring behind it?