CAN anyone please tell me how to stop unwanted telephone calls?

I am registered with the Telephone Preference Service and have used a call blocker, asked for my details to be removed from their system, put the phone down on them, and not answered any number I do not recognise, but still they keep coming.

Callers refusing to take no for an answer when asked to take part in another survey, and today I have had a call regarding my computer. What computer?

What can I expect next? Calls about funeral plans when I am nursing my husband through a terminal illness, or more pet plans when I have just had to have my beloved dog put to sleep?

I try to be polite but I will not be responsible for my language next time.

Name and address supplied