I don't know if anyone can help, I have been trying to get a fault sorted for my 80 year old aunty.
she can make out going calls, but when you ring her number, the phone in the house,gives one very short, very quite ring and unless you are stood by the phone, it's impossible to hear.
I have been to her house ,( 60 miles from my home ) with one of my phones to check if the fault was with her equipment, sorry to say the fault is there with mine aswell.
I rang the faults line on sunday, they were no help at all, because they were asking me to test from the main socket, this unfortunatly can not been done, as the phone line was installed in the 1970's and bt didn't use the master socket system then, but unfortunatly India can not grasp this at all, i have rang them again and again, finally told on tuesday the fault is in the exchange and would be sorted within 24hrs, 72hrs later still not sorted, what do you have to do to get a result with these people.
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It will more than likely be a Rectified Loop fault on the line, your aunt will have a master socket, it will just be the old LJU and not an NTE5a. If you have tested an alternative working phone like you said and its still faulty then you will need to get an engineer out from Openreach to fix it.