True Call, stops it all.
I got so fed up of them, even swearing at them made no difference. I do not mean saying my goodness either, I mean really ripping into them. People we know call our mobiles., I considered having the landline cut off, until I discovered True Call. Bought one (first landline phone I ever paid for), installed it, and thought it was broke, was ringing people asking them to call me to see if the phone works. Not a single spam or telesales call since, fantastic, cannot praise them enough, and never had a problem with them. BT are the best, I have just replaced my triple set with the new premium, just because I wanted to, worth every single penny.
https://www.argos.co.uk/product/8203081