Who called from 2132712852

Phone rings once from 213-271-2852 every half hour or so.  Does anyone know who these people are?

(213) 271-2852
Type: Land Line
Provider: MCI Worldcom Communications Inc
Location: Los Angeles, CA
Due to number portability, some numbers have been transferred to a new service provider.
Type: Land LineProvider: MCI Worldcom Communications IncLocation: Los Angeles, CA

rings my cell phone about every half hour, doesn't leave a message...just rings and rings until the call cuts off.

no message left, when you answer there is no one there.  Called 16 times so far today.

This phone number has been calling one of my cell phones every few minutes! I read on our Cell home page that incoming calls cannot be blocked. Is there anything we could do to stop this annoying call?