how do they know my home phone number?

I often gave out my landline number without thinking too much.  The consequence is that I got lots of phone calls day and night at around home and car insurance renewal dates.  it was quite annoying.So I decided to change it  from bt to sky. Since then Only my family, relatives and close friends know my new home number. If the bank, insurance company or others asked I only give my mobile number.

However Yesterday I got a strange call through home phone,  3 years after a car accident and claimed about 2000 pounds for injury,  a man from injury claim company asked if my neck still sore. 

How does he know my home phone number?