I never answer calls with an unrecognised number ...just make a note of it from the phone display and check it online ...always on the 'liste rouge' ...not known to anyone ! OH answered the phone one morning when I was out ....someone said 'You have a problem with your computer' (now he doesn't use a computer ...bought himself one to learn on, couldn't find the on button, or, as he said, the 'button marked 'click' and so he gave up !.....) anyway, that morning the guy said 'you have a problem on your Orange (our provider) computer ....so he duly took the phone into my office, and told the called (quite genuinely) ...sorry, my wife has a silver computer and a black one, but I cannot see an orange one .....no idea why they hung up on him .......but I might just use the same tactic !