Don't know how much this will help, but here goes...
If your Mum has TPS, report the calls anyway, even with the lack of information she has. Others may have complained too and TPS may be able to investigate.
Report the calls to BT as nuisance calls. I don't have a lot of faith in BT but they do seem to be able to deal with nuisance calls quite well. My Mum had a similar problem and was quite unnerved by it - whether true or not, your Mum should make a point of saying she feels threatened.
Try to identify a pattern in the call times - if that is possible, then let the call go to answerphone if the phone rings around those times.
Finally I'd say that she shouldn't respond to the menu instructions, as this may be seen as a sign of interest by the company and lead to more calls.
Not sure what else to do, though I like your rape alarm idea. Don't forget though that these days she might be the one who gets into trouble.
Your Mum has every sympathy from me. Junk calls are a pestilence.
(eesnahk, Mon 7 Sep 2009, 22:19, 1 reply)

TPS
Yeah, that's seeming like the best option. The fact that this has happened several times and he won't give any details does class it under nuisance. It's not every hour of the day or night (approx twice a week really), but it's definitely enough to be annoying.
(calamarain just invented dehydrated water, Mon 7 Sep 2009, 22:43, closed)