The only way to really prevent it is to allowlist specific numbers you know will call the number and send "Number disconnected" signals for the rest. Eventually, the number gets quieter until it can be reached again.

The ideal setup would be to have a private number that you never give out that denies anyone not on your allow then use throwaway numbers you can turn on and off as you need them.

I used to have it where I would give numbers out then only have them 'active' when I was expecting a call.

My original hypothesis was that the numbers were harvested, my new one (and likely correct) is that numbers are randomly dialed.