Who called from 2132712852

Started a few week ago, and is disconnected before
I get it to my ear....
Calls every 15 min. the last to days....

Unknown number calls cell phone and does not respond when answered.  Since only family has this number,I don't know who this is.

Caller Id:  California,No Message!

(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

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