MD83 CREW HAD SIMILAR CALL SIGN CONFUSION AND MAY HAVE TAKEN CLRNC FOR ANOTHER ACFT IN ZZZ CLASS A AIRSPACE.

Narrative

I WAS THE CAPT FROM ZZZ-ZZA. THE FO WAS FLYING. ACFT (MD83) WAS ON AUTOPLT IN CRUISE LEVEL AT FL350 WHEN THE CTR CTLR GAVE US A CLRNC TO DSND FROM FL350 TO FL310. I READ BACK THE CLRNC; SET THE ALT ALERT TO FL310 AND THE FO ACKNOWLEDGED AND BEGAN A STANDARD RATE DSCNT. CONDITIONS WERE DAYLIGHT AND VMC ON TOP. AS WE BEGAN THE DSCNT WE HEARD THE CTLR REPEATEDLY CALL YYY WITH NO RESPONSE. I BELIEVE THIS WAS AFTER WE BEGAN THE DSCNT. I ALSO BELIEVE YYY; WHICH LANDED 4 MINS AFTER WE DID; WAS BEHIND US. THE TONE OF THE CTLR BECAME INCREASINGLY CONCERNED AND AT ONE POINT I ASKED IF HE WAS CALLING US (XXX). HE REPLIED THAT HE WAS NOT. WHILE THE CTLR WAS CALLING YYY I BELIEVE WE WERE DSNDING THROUGH FL330 OR SLIGHTLY LOWER (FAIRLY SLOW DSCNT); WE RECEIVED A TCASII TA. I QUICKLY LOOKED FOR THE TFC AND SPOTTED AN ACFT APCHING FROM OUR 9 O'CLOCK POS (ABOUT 5-7 MI AWAY). IT APPEARED SLIGHTLY BELOW US (FL310). THE FO BEGAN SLOWING THE DSCNT AND THE TCASII GAVE A 'CLB' ADVISORY. WE IMMEDIATELY BEGAN A CLB UNTIL THE RESOLUTION WAS CLR AND THEN AIRPLANE PASSED BELOW US. I BELIEVE WE MAY HAVE RECLBED TO FL340 IN THE PROCESS. THE CTLR NEVER ACKNOWLEDGED A PROB EVEN THOUGH I ASKED ABOUT THE OTHER AIRPLANE AND WE WERE QUICKLY CHANGED TO THE NEXT SECTOR AND CONTINUED OUR ARR WITH NO ONE COMMENTING. UPON ARR WE CALLED CTR AND TALKED TO THE SUPVR. HE STATED THAT (APPARENTLY) WE HAD TAKEN THE CLRNC FOR THE WRONG AIRPLANE (APPARENTLY YYY) WHICH IS CURIOUS SINCE YYY WAS BEHIND US (WHY WOULD THEY DSND HIM BEFORE US?) IN ANY CASE; HE ACKNOWLEDGED THAT WE HAD READ BACK THE CLRNC (POSSIBLY INCORRECTLY) AND THE CTLR DID NOT CATCH IT. HE SAID HE DIDN'T SEE A PROB FOR US; ALTHOUGH SINCE IT HAD ALSO HAPPENED THE PREVIOUS WK; HE INTENDED TO CALL ACR AND ASK THEM TO CHANGE THE FLT NUMBER. WE AGREED THAT WAS A GOOD COURSE OF ACTION. NEITHER THE FO NOR MYSELF BELIEVE THAT WE TOOK THE WRONG CLRNC (BECAUSE WE BOTH HEARD OUR NUMBER AND BECAUSE YYY WAS BEHIND US -- AND FOLLOWING THE INCIDENT; THE CTLR SAID NOTHING ABOUT OUR ALT -- NOR DID THE NEXT SECTOR SAY ANYTHING). IN RETROSPECT; THESE 2 NUMBERS XXX AND YYY WERE AN EXTREMELY DIFFICULT COMBINATION. EVEN AFTER THE PROB; AS WE CONTINUED TO DEST IT WAS VERY DIFFICULT (NOW THAT WE WERE PARTICULARLY TUNED TO THE DISCREPANCY) TO DISTINGUISH THE 2 CALL SIGNS. PS-- AFTER RECEIVING MORE DETAILS; WHAT THE SUPVR HAD NOT TOLD US; APPARENTLY THE CTLR HAD GIVEN US (XXX) A FREQ CHANGE; WHICH WAS MISTAKENLY TAKEN BY YYY (BEHIND US). THAT EXPLAINS WHY HE WASN'T ON THE FREQ; BUT IT DOESN'T EXPLAIN WHY CTLR DSNDED YYY BEFORE US AND WHY THE CTLR DIDN'T CATCH THE MISTAKE (THAT WE WERE STILL ON THEIR FREQ) WHEN I ASKED IF HE WAS LOOKING FOR XXX.