It is a horrible thing to happen and can be quite frightening if living alone.
Back in the past, these sort of calls, or just plain dirty ones, was far more common, as no caller number came up.
There are a couple of ways of dealing with this sort of thing. Firstly, let all incoming calls go to answerphone, then you can decide if you want to talk to whoever is calling.
Otherwise have some of your own fun with them. I would never do anything cruel and dangerous, like blowing a whistle down the phone, but my favourite withe dirty callers was to say EXTREMELY LOUDLY ' SORRY, I HAVE LOST MY HEARING AIDS AND CANNOT HEAR YOU, PLEASE SPEAK VERY LOUDLY'.
Then however, loudly they spoke I would interrupt to say still could not hear and understand them, could they please shout louder. You will be pleasantly surprised as to how quickly they ring off and never bother to ring back!!!