A B757 CREW RPTED THAT; WHILE ON THE ROBBINSVILLE STAR INTO EWR; THEY RECEIVED AND ACKNOWLEDGED A SERIES OF CLRNCS THAT ZNY LATER SAID WAS FOR A COMPANY ACFT WITH TWO OF THE SAME FLT NUMBERS. THE PLTS BOTH CLAIM THAT NO SUCH ACFT WAS IN THEIR AIRSPACE; NOR DID A COMPANY LAND AT EWR WITH SUCH A CALL SIGN.

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ZNY CLRED ACR 123 TO CROSS HOLEY AT 11000 FT. THE CAPT READ THE CLRNC BACK AND I STARTED DOWN TO CROSS HOLEY AT 11000 FT. AT ABOUT 13000 FT THERE WAS A GARBLED XMISSION AND SOMEONE SAID; 'CTR; YOU WERE STEPPED ON' AND ATC SAID; 'ACR 123; CROSS RBV AT 8000 FT.' THE CAPT READ BACK THE CLRNC OF; 'ACR 123 CROSS RBV AT 8000 FT;' AT THAT TIME I SET 8000 FT IN THE ALT WINDOW ON THE MCP. THE CAPT CONFIRMED THE 8000 FT ALT AND I STARTED TO SLOW TO 250 KTS; CONTINUED THE DSCNT TO CROSS RBV AT 8000 FT. AS WE (ACR 123) DSNDED THROUGH ABOUT 10000 FT; ATC SAID; 'ACR 123; WHAT ALT ARE YOU AT? I (ATC) SHOW 10000 FT AND I ONLY CLRED YOU TO 11000 FT.' THE CAPT REPLIED; 'ACR 123 IS OUT OF 10000 FT TO CROSS RBV AT 8000 FT AS CLRED.' ATC REPLIED; 'RBV AT 8000 FT WAS FOR ACR 23 AND NOT YOU ACR 123.' (AT NO TIME DID WE HEAR ANY ACR 23 ON THE FREQ OR WERE WE ADVISED THAT A COMPANY ACFT WOULD BE ON THE FREQ.) THEN ATC SAID; 'ACR 123; CROSS RBV AT 8000 FT.' WE CONTINUED TO EWR AND LANDED. SUPPLEMENTAL INFO FROM ACN 464940: DSNDING ON THE ROBBINSVILLE ARR INTO NEWARK; FLT 123 WAS INITIALLY GIVEN; 'CROSS HOLEY AT 11000 FT.' THERE WAS NO CONFLICT PROB. HOWEVER; THERE WAS NO ACFT 23 ON THE FREQ NOR ONE ARRIVING AT NEWARK.