First of all, thank you for your kind donation.
I am pleased that your flat is snagged and fixed.
By the way it doesn't matter how old a post is, as the same problems often re occur.
BT would normally only connect up the main master socket (where the outside BT cable enters the property). All other telephone sockets are extensions provided by the housebuilder and should be connected by them.
Most telephone engineers do connect the extension cable(s) in the master socket as well as the BT cable but they don't have to.
I would ask that the site electrician calls round one evening to do this for you.
It is certainly not a £50 - £150 job, about 10minutes maximum.
One more thing, did you know that PlusNet was bought by BT?
BT tell me that they are run as separate companies though!!
In fact anyone who is reasonably capable with DIY should be able to do it.
Look online for help, perhaps this will help.