If these scammers use a business phone system, blocking your phone number would probably be ineffective. Calling back carries risk and is a controversial subject here for several reasons (number spoofing, confirming a live person is at the end of your phone number, retaliation by spoofing your phone number and making scam calls).
I recommend not wasting your time calling scumbags. But if you must, buy a "burner" phone or pre-paid SIM so your actual number isn't as easily associated with you. Just be courteous and hold on to the number; the next poor soul getting assigned your mobile number can end up being blasted by scammers.
Just checked my cell phone this morning at 7:02am. There's a missed call from 754-307-0900 that came in at 6:31am! I missed the call so that's all I know. If it's a telemarketer, this is an illegal call.
I called this number back and it was Jason from Career Services. He asked is Michael there? Then I hung up. For all we know it could be some sort of scam. This call is from Pompano Beach FL. Why would this guy be calling me? I am looking for work in IN not in FL. I most certainly did not request services from these people. They must got my name off of a sales list or through an online phone book. My number is not in the telephone directory. They must have got it off of my Facebook. I better take it off of there before every major telemarketing company starts calling me.
You know it's crap-call when they call a fresh number not used. Amazing but we just got a 2nd phone number here, and this trash calls are incoming. Thank to this website, it makes it easy to ban future calls. We all have busy days and having your day/night disturbed by these aggressive marketeers is totally BS.