Who called from 2157100083

This number keeps calling my cell phone and doesn't leave a message

Called my cell phone.  Did not answer.  Left no message.

Called my cell phone.  Answer, but no one on the other end

got a call. The number looked strange to me. Have not answered. And not regretting.

Called number back and turns out its Comcast. I'm guessing an upsell call, cause billing is up to date.