I had one 2 days after my accident. They knew my name, mobile number and that I had been knocked off my bike by a car. I don't know how they got it. The people who had that info were the woman who knocked me off, the policewoman, Slater Gordon, a few friends and relations, and Admiral -the driver's insurers. That's quite a long list now I've written it down. I'm not sure why Admiral as a company would want to share that info with a company with whom they might have to go into negotiations, but I suppose that doesn't necessarily go for any disreputable employees they may have.
One particularly insidious thing was that they introduced themselves as being from 'the aftercare team' and I was expecting a call from a Slater Gordon solicitor. This confused me for a while until I realized it was 'The Aftercare Team' was a bunch of ambulance chasers. I've had a few more since but they seem to have stopped now.
Sorry, no advice as to how to stop them.