Ofcom's advice on your next step

Problems with your landline phone -
Privacy issues - nuisance and sales calls and faxes

Malicious or nuisance calls, whether from people you know or from complete strangers, are a criminal offence.

You should tell your phone company as soon as you receive a malicious or nuisance call from somebody. It doesn’t matter whether you know the caller’s identity or not.

Phone the operator and ask for the number of your company’s nuisance or malicious calls team. Then tell the team that you have received a malicious or nuisance call from somebody. Tell the team what the caller said.

In some cases, particularly if the caller is threatening, your phone company will advise you to call the police. If the caller is making direct threats to you or your family and you believe those threats to be real and immediate, then you must call 999 straight away. However, if you believe that the threats made are not immediate, then you should call your local police station on their normal local telephone number.