A couple of points (from an old age pensioner), they may not be relevant, but, will do no harm:
- Have you registered your mother's telephone number with TPS (telephone preference service)? It is not perfect, but, does cut down the number of nuisance calls. (a similar service exists for junk mail, called, predictably, MPS).
- Have you considered speaking to her telephone service provider to have her number changed, if they (the scammers) don't have her number, they cannot ring her. Sadly, I believe there is a "market" in telephone numbers of vulnerable people, so, her number may well being passed on.
From personal experience, with my late mother, I think a factor is, that generation were much less likely to challenge "authority", and, much less likely to be blunt and/or rude. Not problems I personally have (at present).