The scammers are usually are sitting in a call center (in Asia usually.) However if they would call from that number people won’t pick it up or would not believe that it is Amazon, Microsoft or your bank. This is the reason they are pretending to be calling from an another (local) number. They can do this using a loophole in the roaming system. So this why you can receive calls pretending by to be your contact’s number or even from your own number. This is why just blocking those numbers is not that effective. Also if you call the number back, it is not the scammer, just a normal person or business with that number. Hope this explains it.