FLC OF AN MD88 WERE GIVEN CLRNC TO HIGHER CRUISE ALT; FOR WHICH THEY HAD FILED AND EXPECTED. HOWEVER; ARTCC CTLR INTERVENED DURING THEIR CLB AND SAID THAT THE CLRNC WAS FOR ANOTHER ACFT. THEY THEN LEARNED THAT THE OTHER ACFT HAD A SIMILAR SOUNDING CALL SIGN BUT THAT THE CTLR DID NOT USE THAT ATC PROC WHEN GIVING THE CLRNC.

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AT CRUISE FL290 WE CALLED ZJX AND ASKED IF FL290 WOULD BE OUR FINAL. THE CTLR RESPONDED THAT WE COULD EXPECT FL330 (OUR FILED CRUISE WAS FL330). A SHORT WHILE LATER; WE HEARD ACR X CLRED TO FL330. WE READ BACK 'ACR X DEPARTING FL290 FOR FL330.' WE SET THE ALT ALERT TO FL330 WITH THE OTHER PLT VERIFYING THE ENTRY. WE BEGAN OUR CLB TO FL330. PASSING APPROX FL310 WE HEARD ZJX SAY THAT THE CLRNC TO FL330 WAS FOR ACR Y. WE THEN ASKED THE CTLR WHAT ALT ACR X WAS TO MAINTAIN; AND HIS REPLY WAS FL290. WE IMMEDIATELY BEGAN A DSCNT TO FL290 ATTAINING A MAX ALT OF FL313. NO MENTION WAS MADE BY THE CTLR FOR US TO DSND TO FL290. THE TCASII LOOKED CLR OF TFC IN OUR VICINITY. IN OUR DSCNT TO FL290 WE AGAIN VERIFIED OUR CORRECT CRUISE ALT OF FL290 WITH THE CTLR AND WAS TOLD TO MAINTAIN FL290; WHICH WE DID. DURING ALL OF THIS; THERE SEEMED TO BE A LOT OF CONFUSION BTWN US; THE AIR TFC CTLR; AND ACR Y FLT. ACR Y EVEN SEEMED SURPRISED TO BE TOLD THAT HE HAD BEEN CLRED TO FL330. AS WE RECEIVED A FREQ CHANGE; I INFORMED THE CTLR THAT WE HAD RECEIVED THE CLRNC TO FL330 FOR ACR X AND READ IT BACK THAT WAY. THE CTLR'S REPLY WAS 'WHATEVER.' I THEN INFORMED THE CTLR THAT HIS REPLY WAS NOT VERY PROFESSIONAL. THERE WAS NO CONFLICT WITH ANY OTHER ACFT DURING OUR DEV; JUST A LOT OF CONFUSION. THE CTLR COULD HAVE HELPED ALL INVOLVED BY TAKING CHARGE AND TELLING EACH ACFT WHERE HE WANTED US SINCE HE WAS THE ONLY ONE WHO KNEW WHERE EACH ACFT WAS TO BE. AT NO TIME WAS THERE ANY MENTION OF SIMILAR SOUNDING CALL SIGNS ON THE SAME FREQ NOR DID WE HEAR ACR Y FLT TALK ON THE FREQ PRIOR TO THE PROB.