Let it ring. Robocall centers only work when they maximize volume, the more time they spend not getting an answer the more money they’re not making. If you wanna get real saucy, wait as long as you can, accept the call, say nothing or mute your mic. They wont spend more than 5-10 seconds before they hang up on you though because they know it too.
Letting it ring has no impact. They have autodiallers that call, and when someone picks up, only then is that call assigned to someone in the call centre.
You can often tell this because there is a marked delay in the response to your initial “Hello?”. Long enough that you can reliably just hang up if you don’t hear a response in two seconds.
If it’s a real person who actually wants to call you and they you call again straight away, you can just shrug off your hang-up as a network issue.