Telephone problem

[Gavmacp]

I ring my mother twice and she rings me back using the last number device on her phone. This works fine until she gets a cold call. Then I ring her she does the same my phone rings but she does not appear to be there. If she does the same again again I cannot hear here.
Does anyone else have this problem or even more importantly any solution.

[AlBags]

Probably because the spam call is automated, and holds onto the line for a few minutes.
Just a guess.

[boxtops]

Yes, she ought to leave it five minutes before she tries to use the line again.

[Old_Geezer]

If the cold caller was still holding the line then you could not have called her, the line would have been engaged, so I don't recognise the other explanations. But have to say I can not think of a reason for this experience. That's really weird.