When I first got my new phone number, apparently it had quite recently belonged to someone else.
This was many years ago and ATT didn’t have call blocking. But with caller ID I coukd see that they were a foreign area code (turned out it was Africa)
So, whenever one of those calls came in, I would connect to it but not say a word. I would then keep the line active but not say a word and just let it sit that way until eventually they just hung up.
Since I had unlimited on my cell and they were calling from overseas, it cost me nothing but must be costing them something no matter how little.
Plus, a lot of them get paid on commission so wasting time trying to talk with absolutely no response from the other end is wasting time they could be spending annoying someone else.
It only took a few weeks of the silent treatment for my number to be put in the “not worth bothering with” list and I’ve never gotten another call like that since.
Since you can’t use the loud horn method, perhaps the totally silent treatment will be frustrating enough for them. So, just use that consistently and see if it helps.
But, you do have to train yourself out of the habit of saying anything as soon as you pick up the call. If it’s a legitimate call, they’ll say something first and identify themselves. So saying nothing at all is unlikely to really cost you calls with someone you really do want to speak to.
This whole silent thing worked far better for me than I could have hoped. Hopefully it will help you out as well.