OPERROR LTSS WHEN 2 OPPOSITE DIRECTION E120'S WERE AT THE SAME ALT.

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WE WERE ABOUT 30 MI NW OF FRESNO LEVEL AT 13000 FT GOING TO FRESNO YOSEMITE INTL ARPT. OUR CALL SIGN WAS ACR X. CTR STARTED TO GIVE US A TA OF COMPANY ACFT ACR Y 10 MI AWAY COMING IN THE OPPOSITE DIRECTION WHEN HE REALIZED THAT THEY WERE ALSO AT 13000 FT. BOTH ACFT VERIFIED THEY WERE AT 13000 FT. THERE WAS A BLOCKED XMISSION ENDING IN 'IMMEDIATELY' -- PROBABLY A DSCNT CLRNC FOR ACR Y. THERE WAS NO RESPONSE FROM ACR Y AND NO RECLRNC FROM CTR. THIS WAS FOLLOWED BY A DISCUSSION OF WHETHER ACR Y WAS PREVIOUSLY CLRED TO 13000 FT OR 12000 FT AND WHO GAVE THEM THE CLRNC. BY THIS TIME I SAW ACR Y AND TOLD CTR I COULD MAINTAIN VISUAL SEPARATION WITH THEM. CTR SAID 'OH GOOD.' ABOUT THIS TIME CTR REALIZED THAT BOTH ACFT WERE STILL LEVEL AT 13000 FT AND BOTH ACFT VERIFIED THEY WERE STILL AT 13000 FT. THERE WAS SOME CONFUSION WITH THE CALL SIGNS. CTR GAVE A CLRNC; USING WRONG CALL SIGN; TO DSND IMMEDIATELY TO 12000 FT. THIS CLRNC WAS PROBABLY ANOTHER CLRNC FOR ACR Y; BUT AGAIN THERE IS NO RESPONSE FROM ACR Y AND NO RECLRNC FROM CTR. BECAUSE WE WERE THE ARR ACFT AND WE HAD ACR Y IN SIGHT; IT SEEMED LIKE THE BEST MANEUVER WAS FOR US TO DSND SO WE COULD KEEP ACR Y IN SIGHT AND GET OUT OF THEIR WAY. SO I SAID; 'ACR X IS DSNDING TO 12000 FT.' WHEN ACR Y PASSED US; THEY WERE ABOUT 1 1/2 MI TO OUR L AND 500 FT HIGHER. AS WE WERE DSNDING THROUGH 12500 FT; CTR SAID 'ACR X SAY ALT' AND I RESPONDED THAT WE WERE AT 12500 FT DSNDING TO 12000 FT. CTR SAID 'ACR X CLB AND MAINTAIN 13000 FT' BUT BEFORE I COULD RESPOND HE SAID 'DISREGARD; DSND AND MAINTAIN 11000 FT AND CONTACT FAT APCH.' WE DID NOT MAKE ANY ABRUPT MANEUVERS AND CTR DID NOT ASK US TO PHONE HIM AFTER LNDG.