Besides reporting these types of calls, use your phone settings to block calls from them. I created a dummy contact called Crap and set my phone to block calls from Crap. When another one of these calls comes in, I just add the number to the contact info for Crap.
Just got a call from this number and let it go to voicemail. Idiot on the other end forgot to hang up I guess because there was a 20 second voicemail that sounded like a crowded room before they hung up. No recording, no request to press any numbers, just lots and lots of inarticulate babble. Don't know who they are and don't care, still not going to answer their calls.