I am again in touch, by phone, with BT Mobile tech support team as this has become a potentially life threatening problem.
My wife is unable to contact her doctors as whenever they return her call she misses it because we only get 15 seconds before it goes to voicemail and, try as she may, she is always more than 15 seconds away from her phone when they return her call.
Tech support are sympathetic and are looking into at least increasing the number of rings before it goes to voicemail.
If my wife can't make contact with her doctors we might have to cancel our holiday and return home early.
I can't fault the willingness of the, first class, BT support staff to assist but there's not much they can do about it as it seems to be a management decision to live with the problem and classify it as a feature.
When I phoned this morning, I opened with "I doubt that you will have heard about this problem", sure enough he hadn't, but having read some of the copious notes on my account he said he will be bringing it to the attention of his supervisor.
Having heard nothing further from tech support and still being unable to contact her doctor, my wife is on her way back to the UK.