I once gave our telco/internet provider the permission to call me on my main number if they have an interesting update regarding our contract. That went without problems for over ten years. One or two calls a year, and usually something worth thinking about.

Then their marketing decided to pull all stops and call us, on all our numbers, not just the main one, but also the kids personal phones. And not only from their official numbers, but random numbers all over the country. We suddenly got a dozen calls a day(!) from them, offering the same two products (at least where we picked up and declined the offer) again, and again, and over again. We blocked numbers, and new ones came up. The block list went from two entries to over thirty. I had to threaten legal action got get our numbers blocked again, and get them marked as such according to our privacy laws.

Silence returned.