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.