Some people keep a whistle by your phone so when they get a cold caller –they give them a quick blast.

Some people keep a radio near the phone so they can switch on a noisy station, put the phone by the radio and leave it.

If you can do animal impressions – then why not bark loudly or grunt loudly.

You could record a brass band or some other noisy music and play it when the cold caller phones

You could shout “Sorry . I’m a bit deaf, Can you repeat that”

Alternatively, stand back from the phone and have a good scream – that should send them running and will make you feel better.