Who did she actually call? It's just that Open Reach work for any service provider, they don't work for "Joe public"
Your customer should call her phone provider and ask them.
Yes, I know it's confusing, but since they became 2 companies (2017) One has to ask the other to do something.
It...
I understand your pain, but what you have to appreciate is most modern "devices" have "inbuilt quirks" (For want of a better word) and unless you know what they are you will assume "Part X" is at fault, when it isn't.
Example: You put clothes in a washing machine, close the door, switch it on...
I understand that we all like to help 🥸, but It never achieves anything by guessing/changing random parts. Most things today require specialist knowledge/insight.
Like having a daylight sensor that will not switch on lights, "but it used to, and I have changed the lights and sensor, and it...
Back in T'day before battery load test meters, if T' battery being charged was drawing more than T' 20mA I changed it.
You said you got it from Screwfix, they don't have a high turn over of batteries, how old is the battery itself? Look at its serial number (on the top adjacent one terminal)...
Worth checking are the fuses tight. I have previously had panels where all looks ok, but fuse holder had 0.5mm gap at one end, so it looks ok, works sometimes. Solution: Take fuses out in turn, pinch holder together both, ends put fuse back (obviously)
Also, Texecom have had a lot of poorly...
You have guessed right.
The "day" light should be on constant. If it's flashing either the battery voltage is too low or no mains.
How old is the battery?
I bet it did not work before you changed the CU.
Why bother with an override switch if you know the contactor works?
I would check the voltage at the light with the other two on.
Check all phones, do they have dial tone?
Have you still got a means of testing voltage?
(Old socket) Check the blue/white blue/white on terminals marked A and B I will guess it's 50v
(New socket) If so, connect these to 2 & 5 (doesn't matter which way round)
Check other extensions in house...
You would have hoped so. Try it in a known working socket, see what it does, then if it shows all being well, remove the neutral and then see what it does. (I suspect it will not indicate a lost neutral)