Blocking spam calls when real source number isn't displayed on caller ID
I'm getting numerous spam calls from the same number every day on my AT&T Prepaid flip-phone. At least, it appears as the same number when I check my usage online. When I view the number with caller ID on my phone, it displays with my own area code and prefix, but the last four digits vary every time. I have tried blocking these calls, but that doesn't work. Is there some way to block a specific "source" number, even if it doesn't show up on an incoming call? Help! I've had twenty calls in less than a week!