MD88 FLC ISSUED NUMEROUS HDG CHANGES DURING CRUISE.

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WHILE IN CRUISE AT FL330; ZID CTLR GAVE US INSTRUCTIONS TO TURN R 15 DEGS FOR TFC. WE WERE ON THIS VECTOR FOR APPROX 2 MINS WHEN WE WERE GIVEN INSTRUCTIONS TO PROCEED DIRECT TO EWC. SHORTLY AFTER PROCEEDING DIRECT; WE WERE GIVEN INSTRUCTIONS TO TURN L 15 DEGS FOR TFC. WE COMPLIED AND THEN RECEIVED INSTRUCTIONS TO QUICKLY TURN R TO HDG 140 DEGS (APPROX 100 DEG HDG CHANGE) WITH NO EXPLANATION. NO ACFT APPEARED ON TCASII AND WE RECEIVED NO TCASII WARNING. WHILE IN THE TURN TO HDG 140 DEGS; CTLR ASKED US TO INCREASE TURN RATE AND WE COMPLIED. WHEN WE QUERIED CTLR AS TO WHAT WAS GOING ON; SHE PROVIDED NO EXPLANATION AND SEEMED TO BE A BIT FLUSTERED. AFTER FLYING HDG 140 DEGS WE WERE AGAIN CLRED DIRECT TO EWC AND ASKED TO SWITCH TO NEXT CTLR AND TOLD 'THANKS FOR YOUR HELP.' WE QUERIED NEXT CTLR ABOUT WHAT HAD HAPPENED. HOWEVER; SHE SAID SHE WAS TOO BUSY TO SEE AND DIDN'T KNOW ANYTHING. BOTH I AND FO VERIFIED INSTRUCTIONS FROM ATC AND AT NO TIME WERE WE IN DISAGREEMENT ABOUT CTLR-ISSUED INSTRUCTIONS. WE BOTH FELT CTLR EITHER FAILED TO GET HDOF TO NEXT CTR CTLR AND/OR HAD NEAR LOSS OF SEPARATION. HOWEVER; WE NEVER SAW ANOTHER ACFT IN CLOSE PROX TO OUR ACFT; NOR WERE WE WERE ISSUED A TA.