I'm not sure where to start here, possibly the beginning!
About twelve years ago I started recieving silent phone calls, initially from a mobile & then later from a withheld number! During one evening this individual telephoned me 24 times!!
These calls went on for six years & in amongst the withheld calls were calls mase from Cornwall and a local supermarket.
Why would you tolerate this for 12 years? Ever thought that changing your phone number would solve the problem?
If they are still continuing you need to contact the police and your telephone provider so they can trace the person/s and possible prosecute them.