Forwarding Calls in Consumer Cellular

I have an iPhone XR. I use RoboKiller to screen incoming calls. It doesn't work using the number RoboKiller attempts to uses to set up phone, i.e. **21*, the 10-digit number, and #. Nor does it work using **002* as suggested. I've contacted the J.D. Power award winning Consumer Cellular customer service twice with no response. Any suggestions? Thank you.