FLC OF A WDB OVERSHOT DSCNT ALT DUE TO COPYING THE WRONG CLRNC. ATC INTERVENED AND STOPPED THEM EARLY AND THEN IMMEDIATELY CLRED THEM FURTHER.

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WE WERE DSNDING INTO MIAMI; WE WERE ABOUT 20 MI NE OF THE ARPT PASSING 10000 FT WHEN ATC GAVE US A CLRNC HDG 250 DEGS DSND DOWN TO 2000 FT. I READ BACK THE CLRNC HDG; 250 DEGS DOWN TO 2000 FT; AND THE CTLR SAID ROGER. THE CAPT HEARD THE SAME CLRNC AND HEARD ME READ BACK THE CLRNC AND SOON AFTER HE WAS DISTRACTED BY AUTOTHROTTLES DISENGAGING. SO HE KEPT ON DSNDING DOWN TO 2000 FT AND TRYING TO CORRECT THE AUTOTHROTTLE SYS WHILE I WAS MONITORING THE RADIO. THE FE DID NOT HEAR THE CLRNC BECAUSE HE WAS BUSY CALCULATING APCH SPDS AND SETTING HIS PANEL FOR LNDG. AROUND 4500 FT ATC QUERIED US; FLT SAY ALT. I RESPONDED 4500 FT DOWN 2000 FT. HE SAID NEGATIVE THE CLRNC WAS 8000 FT LEVEL OFF AT 3000 FT. I RESPONDED; WE WERE GIVEN A CLRNC OF 2000 FT; I READ IT BACK AND YOU ACKNOWLEDGED ROGER. THE CLRNC SEEMED CORRECT BECAUSE WE WERE ALMOST ON DOWNWIND AROUND 10 MI FROM THE ARPT. THERE WERE NO ACFT ON TCASII OR ANY ACFT IN THE AREA; TFC WAS LIGHT. THERE WERE 'NO CONFLICTS WITH OTHER TFC' AND WE LANDED WITHOUT FURTHER INCIDENTS. I THINK WHEN ATC GIVES US MULTIPLE CLRNCS; IE; HDG 250 DEGS DOWN 2000 FT; WE NEED TO RESPOND TO EACH ONE INDIVIDUALLY SO HE KNOWS WE FULLY UNDERSTAND EACH INDIVIDUAL CLRNC SO WHEN HE SAYS HEADING RESPOND TO THE HEADING CLRNC AND THEN AFTER HE HAS HEARD THE CORRECT HEADING THEN RESPOND TO THE ALT CLRNC UNTIL HE HEARS YOU RESPOND TO THE CORRECT CLRNC AND PLEASE GET THESE GUYS TO SLOW DOWN; THEY SPEAK ENTIRELY WAY TOO FAST. THANKS FOR YOUR ATTN IN THIS MATTER.