Sky television and police are warning people not to be taken in by scammers purporting to be calling from the broadcaster.
The warning comes after a Sutton woman was called at home by someone claiming to be from Sky.
The caller said the expiry date on her Sky viewing card was coming up and they would need financial details from her in order to renew it.
The woman became suspicious when the caller asked her for her bank details and when she said she would not give her sort code over the phone, the caller hung up.
A spokesman for Sky said the company does not make calls like that.
He added: "Sky viewing cards do not have an expiry date, so we would not contact customers to say that they are about to run out.
"We also don't make outbound calls to Sky customers to request financial information over the phone in this way.
"If customers are ever in doubt about whether a call is genuine, they should end the call immediately. We also have information on our website for customers about handling nuisance calls."
If you have any concerns about a phone call to your landline or mobile, you can contact police on 101.