Its DACS (Digital Access Carrier System) not DAX.
It is a technology developed by BT in the 60's to provide two phone circuits over one physical line by splitting the two voice services into analogue and digital so both people could use the line at the same time as opposed to the really old party line where if the person you shared the line with was on the phone you had to wait for them to get off it before you could use it.
Also if you have cancelled the the order you will now never get a phone line because complaint or no complaint Openreach won't install any physical infrastructure for no reason.
cut a long story short it took 5 months and three failed engineers visits (without being informed so we took time of work etc. to be there) to get receive no service whatsoever (we were never connected and never received a satisfactory explanation as to what the real problems were).
In sheer frustration I cancelled the contract over the phone and now have been presented with a bill of over £200 as our "service" was cancelled within the term of the contract. I ask you do you consider this to be fair? BT are literally asking for money for almost nothing. If anything I should be charging them for the time we took off work, the cost of arranged childcare and the emotional frustration of being without even a landline phone for over 5 months.
If you would like to contact one of the UK based BT Care Team who moderate this forum, they should be able to find out what happened.
They can be contacted using this link BT Care Team
They normally respond by phone or e-mail, within three working days, however you should get an immediate confirmation, with a tracking number.
I can empathise; I'm in a very similar situation to you but have been waiting for over 9 months for a landline. No mobile reception either, 3 miles from the nearest village, 2 young children and a baby, husband (me) often away and incredibly worried when I am. I've just posted some horrific tales from my recent experiences with BT.
Like you, I'm not sure what good my presence here will do, but I know that we should not stand for this service from a virtual monopoly. The Ombudsman can be sidestepped by BT subcontracting the installation to Openreach and 'keeping the customer informed' (monthly texts in my case) therefore are toothless. My MP has been helpful and I would encourage anyone in this situation to contact theirs.
Good luck in the meantime!