NEVER answer or HANG UP.

Surely you know that spam calls are managed by a machine and distributed to a group of people or made by the system itself. The famous "they call and hang up/don't speak" calls are calls that are not answered because the call center operator is on another call when assigned the next one. Therefore, the best thing to do is two things: 1. Do not answer any calls from numbers not in your contacts, unless you are expecting a call (remember that most call centers call from numbers starting with 90X). 2. DO NOT ANSWER OR HANG UP. In both cases, you are telling the system that someone is at that number. And it will keep it "alive" in its database. But if you let it ring until the machine hangs up, eventually your number's category will decrease until it is declared inactive and the system stops insisting. It will take about a month of patience ignoring the calls (I just put the phone face down and leave it) but eventually call centers stop "wasting time" on numbers where "no one is there." This method gives me fantastic results although sometimes call centers revive all the dead numbers. I've had three or four calls per week using this method. But it requires patience.