AN RJCL-65 DSNDED TO 11000 FT MSL. AFTER LEVELOFF; CTR CTLR DISPUTED ORIGINAL CLRNC AND RECLRED FLC TO NEW HDG AND ALT IN DTW AREA.

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WE RECEIVED A CLRNC FROM ZOB TO DSND TO 11000 FT. I PUT THE ALT IN THE ALT PRESELECT; READ BACK THE CLRNC; AND THE FO (PF) VERIFIED IT AND INITIATED THE DSCNT. SHORTLY THEREAFTER; WE WERE ISSUED A FREQ CHANGE TO THE NEXT CTLR; STILL ZOB. WHEN I CHKED ON THE NEW FREQ I STATED; '12500 FT DSNDING TO 11000 FT.' THE CTLR ACKNOWLEDGED THE CALL WITHOUT QUESTION. AS WE LEVELED AT 11000 FT; THE CTLR QUESTIONED OUR ALT AND SAID WE WERE TO HAVE LEVELED AT 12000 FT. AT THAT POINT WE WERE GIVEN AN OFF-AIRWAY VECTOR AND A CLB TO 13000 FT. TO MY KNOWLEDGE; TCASII WAS DISPLAYED ON PIC'S MFD. THERE WAS NO LOSS OF SEPARATION WITH TFC IN OUR VICINITY. CONTRIBUTING FACTORS: 1) BOTH CTR FREQS INVOLVED WERE VERY BUSY HANDLING TFC INBOUND TO DTW. 2) THE SECOND ZOB CTLR (LAST CTLR PRIOR TO HDOF TO DTW APCH) WAS VERY BUSY; AND STARTED ISSUING HOLDING CLRNCS INCLUDING OUR FLT) FOR DTW SHORTLY AFTER HE TOLD US WE WERE SUPPOSED TO BE AT 12000 FT. SUPPLEMENTAL INFO FROM ACN 421559: THE CTLR ACKNOWLEDGED OUR CHK-IN. WHILE LEVELING AT 11000 FT; THE CTLR QUERIED US AND SAID 'YOU GUYS ARE SUPPOSED TO BE AT 12000 FT.' CONTRIBUTING FACTORS: THE WX WAS DETERIORATING. THE CAPT WAS MONITORING TCASII AND THERE WERE NO KNOWN CONFLICTS.