Nuisance calls spoofing local numbers?

[Technical Ben]

I'm now getting 5 calls a day to my mobile, and a couple to my home over some one hitting my car last year. So one of the claims companies (or through a public/easy access database) has given out my details.

It's driving me nuts, not because of the calls, as I'd often spot them and not answer, or in answering give them a little bit of "fun" to deal with (I'm considering Death Vader as my next impression). No, but because they seem to have started to spoof numbers.

I wondered as it was obviously the same recording, but from different numbers each time. Knowing these kind of people are too lazy to actually do the work of setting up hundreds of offices, I'd wondered if it was an automated system. A quick Google shows that yes, a new "feature" allows call centres to display any number as a "Caller ID" so as to "help people call back on a better rate line".  Yeah, so that's not what's happening here, they are abusing it to hide their true identity.

So, just now got a call, and saw it was a local number. Did not get there in time, so dialled back. This is the strange part, it went through to their call centre (can hear in the background), and not a (seemingly) local number. So, how are they doing this then?

On a side note, the guy at the other end got real ratty for me "wasting his time" when I said "sounds great, where is your office, you must be just around the corner, I'll visit tomorrow and we can sign the paperwork".

He offered to email me the details, and told out all my info, I said none of it. All the while telling me how much he "has to keep to data protection so cannot give out the business address or phone number". So, in giving out all my data, without verifying me... I wish I was recording, so I could "drop the books" on this lot. 

How do they do this?

[Clive]

As far as I am aware they use VoIP to display false numbers.  I get them on my landline but the Callblocker can be set up to block them. 

[Technical Ben]

Sounds about right. This is the strange bit though... I called them back (assuming it's a local friend or a neighbour). So how did I get back to them, and not a local number? Or have they bought up a load of old numbers for offices or something?