I've had several of those calls and do what a friend advised me to do. It keeps them talking and wastes their money. It goes something like this.
Tilly2 'Oh, that's interesting. How do you know I've got a problem?'
Them 'Mutter mutter.'
T2 'Yes, but how do you know. You must be really clever?'
Them 'Mutter........'
T2 'I'm really interested in the technology. Do explain it to me, as I think it's amazing.'
etc, etc, etc.
They usually hang up when I get to the bit where I say 'Yes but I still don't understand how you know I've got a problem when I don't even have a computer.'
Try it, it's amusing to hear their frustration.