I think that MPs have missed an important point when they looked at the legislation recently. There is no good reason for any company to withold their number, they should all be legally obliged to reveal it so that we can identify them and tell them to stop or just not pick up at all. A single number leading to an answerphone identifying themselves but taking no messages would be sufficient.
A few times a year I receive up to half a dozen silent calls a day for two to three weeks on my mobile. I cannot get it to stop as too many people, clients, organisations know the number, so I cannot simply change it; the mobile company have identified the caller but cannot contact them for me and can only release the information to the police; and the police refuse to do anything as they receive so many similar complaints. If only they had to reveal their number, I could inform them that their autodialler is malfunctioning!
SteveW