I don't know how it works, I only get like two a month. A friend of mine gets two or three
a day and has just disconnected his phone and advised friends and family to only use his mobile.
The same applies to the large scale phone fraud though, which quickly gets into tens to hundreds of millions of euros per year. Police won't do much because the criminals are outside Germany and cooperating with e.g. Turkey is hard, and with India it's impossible. Phone companies don't care because they're making money and the regulator is asleep at the wheel.
Let's just make the phone companies liable for damages where they can't produce the customer (no KYC) or the customer is international. They'll quickly figure out who is legit and who isn't when it actually hurts their bottom line.