B757-200 CLIMBING OUT OF FL250 WITH ZMA WAS GIVEN UNEXPECTED HOLDING INSTRUCTIONS WITH NO EXPLANATIONS AS TO REASONING.

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APPROX 20 NM NE OF MTH VOR CLBING OUT OF FL250 (ESTIMATED); OUT OF NOWHERE GOT A CALL FROM ZMA CTLR 'ACFT X HOLD N OF MARATHON VOR AT FL300.' QUESTIONS POPPED UP AS TO WAS IT US? WAS THE CALL SIGN MISSTATED? HOLDING DID NOT MAKE SENSE SINCE WE WERE CLRED DIRECT TO MTH VOR AND CLBING TO FL370. THEN ANOTHER CALL ON THE FREQ TO ACFT Y TO HOLD AND THEN ANOTHER FLT TO HOLD. THERE WERE MULTIPLE FLTS ON THE SAME FREQ THAT WERE INSTRUCTED TO HOLD. AGAIN I ASKED CTR IF THE HOLDING INSTRUCTIONS WERE FOR US OR SOMEONE ELSE AND THE CALL SIGN GOT CROSSED OR MISSPOKEN? HOLDING DID NOT MAKE SENSE. THERE WAS LOTS OF CONFUSION ABOUT HOLDING GOING SWBOUND. CTR CTLR DID NOT GIVE A HINT AS TO WHY WE WERE HOLDING. WAS THE HOLDING CLRNC FOR US OR SOMEONE ELSE? WE SET UP HOLDING NOT BEING SURE IF IT WAS FOR US. OUR ALT WINDOW WENT FROM FL370 TO FL300 BACK TO FL370 AND BACK TO FL300. THERE WERE MULTIPLE ACFT ON THE FREQ AND EVERYONE WAS PUZZLED AS TO WHAT WAS GOING ON. WENT OVER TO HAVANA FREQ AND TALKED WITH THEM. THEY HAD NO ANSWER. FINALLY ON MIAMI FREQ; CTLR DEEMED APPROPRIATE TO ADVISE US THAT HE HAD NO PHONE CONTACT WITH HAVANA AND; THEREFORE; DECIDED TO PUT US IN HOLDING. HAVANA WOULD NOT ANSWER THE HDOF LANDLINE SO; THEREFORE; THE HOLDING. TO ME IT WAS A 'DANGEROUS' SITUATION. 'WAS THAT FOR US?' SCENARIO DEVELOPED VERY QUICKLY. HOLDING DID NOT MAKE SENSE! NOT THAT IT'S SUPPOSED TO; BUT IN THE CLBOUT TO FL370 GET HOLDING INSTRUCTIONS. ONE XMISSION FROM THE CTLR WOULD HAVE MADE ALL THE DIFFERENCE IN THE WORLD AND SITUATION MUCH SAFER; IE; 'ALL ACFT HEADING INTO HAVANA AIRSPACE NEED TO HOLD AS INSTRUCTED.' THAT WOULD HAVE ANSWERED ALL THE QUESTION MARKS.