ACR X TOOK DESCENT CLRNC WHICH ATC INTENDED FOR SAME ACR COMPANY FLT Y. READBACK OF CLRNC BY X WAS NOT HEARD BY CTLR.

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ACR X WAS DSNDING FROM FL370 TO FL310. WHEN WE WERE PASSING THROUGH FL320; ZOA GAVE A CLRNC TO DSND AND MAINTAIN 16000' AND TURN RIGHT (FROM OUR CURRENT HDG OF 270 DEGS) TO HDG AT 280 DEGS. THIS WAS A NORMAL CLRNC FOR US TO RECEIVE AT THIS POINT AS WE HAD IN THE PAST. THE CAPT (PNF) READ BACK THIS CLRNC WITH OUR CALL SIGN. THERE WAS NO RESPONSE FROM CENTER (WHICH IS NORMAL WHEN THE READBACK IS CORRECT). AT 30400'; ABOUT 30 SECS AFTER PASSING FL310; ZOA CALLED AND SAID TO MAINTAIN FL310. WE IMMEDIATELY CLBED FROM FL304 BACK TO FL310. THE CAPT ASKED ZOA TO CONFIRM THEY WANTED US BACK AT FL310. ZOA SAID YES. WE RETURNED BACK TO OUR ORIGINAL HDG (270 DEGS) WHILE RETURNING TO FL310. THE CAPT THEN ASKED ZOA ABOUT THE FIRST CLRNC AND THEY SAID IT WAS FOR ANOTHER COMPANY ACFT Y. THE CAPT ASKED ABOUT HIS READBACK OF THAT CLRNC. ZOA SAID THAT THE OTHER COMPANY ACFT WAS ON ANOTHER FREQ AND ITS XMISSION BLOCKED OUT OUR XMISSION SO HE NEVER HEARD IT. ABOUT 1 MIN AFTER RETURNING TO FL310; WE WERE GIVEN A CLRNC TO DSND TO AND MAINTAIN FL180. THE CAPT RESPONDED WITH A READBACK AND OUR CALL SIGN. THERE WAS NO RESPONSE FROM ZOA. THE CAPT READ BACK THE CLRNC A SECOND TIME AND THEN RECEIVED AN ACKNOWLEDGEMENT FROM ZOA. THERE APPEARS TO BE FROM THIS AND OTHER OBSERVED SITUATIONS; A GROWING PROB; ESPECIALLY LATE AT NIGHT; OF CTLRS HAVING TO WORK SEVERAL DISCRETE FREQS AT ONCE AND THEREBY HAVING SOME XMISSIONS TO THEM BLOCKED. SUPPLEMENTAL INFO FROM ACN 95078: PRIOR TO SWITCHING TO RNO APCH I QUESTIONED ZOA AS TO HIS INTENTIONS CONCERNING THIS DEVIATION. HE SAID THERE WAS NO CONFLICT AND NOTHING WOULD BE DONE CONCERNING IT.