CLRNC DISPUTED - THE FLC HEARD AND READBACK THE ALT AND SET IT INTO THE ALT ALERTER. AFTER LEVELOFF THE CTLR SAID THAT IT WAS THE WRONG ALT.

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PHIL FREQ 128.4. ATC CLRED US TO DSND TO 5000 FT AND HDG 120 DEGS VECTORS FOR THE ILS RWY 29 CHESTER COUNTY. I READ BACK 5000 FT TO ATC; DIALED IN 5000 FT ON THE ALT PRESELECT AND VERBALLY SAID 5000 FT SCATTERED. THIS ALLOWS THE PF TO CONFIRM THE ALT TO WHICH WE ARE CLRED. THE PF (ALSO PIC) CONFIRMED 5000 FT AND BEGAN DSCNT. UPON REACHING 5000 FT; ATC IN AN ANNOYING WAY; SAYS WE WERE CLRED TO 6000 FT; BUT SINCE YOU'RE AT 5000 FT STAY THERE AND CONTACT PHL ON 124.35. ON THE GND THE PIC CALLED PHL ATC AND ASKED THAT THE TAPE BE PLAYED. ATC CALLED BACK AND SAID THE ALT CLRED TO ON THE TAPE WAS GARBLED; HOWEVER; MY READBACK OF 5000 FT WAS CLR AND THE CTLR SHOULD HAVE CAUGHT ANY DISCREPANCY. NO CONFLICT WITH OTHER ACFT OCCURRED. I CANNOT THINK OF ANYTHING MORE THE CREW ON THIS FLT COULD HAVE DONE TO PREVENT THIS PROB FROM OCCURRING. I BELIEVE THE PROB OCCURRED BECAUSE: THE CTLR DID NOT REMEMBER CLRING US TO 5000 FT OR THE CTLR DID NOT LISTEN TO MY READBACK OF 5000 FT. SINCE BOTH CREWMEMBERS HEARD 5000 FT; I BELIEVE PROB A OCCURRED. BECAUSE THERE WAS NO CONFLICT WITH OTHER ACFT; THEREFORE NO ALARMS; THE CTLR DID NOT ALERT US OF ANY DISCREPANCIES UNTIL WE HAD ALREADY LEVELED AT 5000 FT.