Harassing landline calls

[Sam+A16]

the past few months, my landline has been bombarded with harassment calls, scam calls, sales calls. All being routed through UK numbers.

i am TPS registered. 
however, I would like to know HOW my number has been leaked. We have NEVER experienced anything like this before. 
I have been extremely careful who I have given this number too (emergencies only). My direct family, work (local government), GP / NHS Services. 
we do not answer the calls as we do not know the number but it is infuriating how this has suddenly started after having zero harassment calls in the past. 

[Daniel0210 · Accepted solution]

@Sam+A16 

It won't have been leaked. Scammers and companies cold calling use machines to generate the calls randomly then if someone picks up they start their patter. Try Sky Talk Shield 

https://www.sky.com/help/articles/sky-talk-shield-start

or get a phone that can block certain calls. 

[Mark39]

Scammers don't need to know your number. They use an automated device to dial every number in a block, in the hope that one or more will be answered. Using the call screening feature of the Sky Talk Shield, available free to most Sky Talk customers, is a way of intercepting these calls to stop you being bothered by them.

[mormegil]

Also if you supplied your number for the electoral roll then it is published freely