ARTCC ARTCC INTRAFAC COORD ACR X TCASII TA ASSIGNED SAME ALT AS ACR Y HAD LTSS. EVASIVE ACTION TAKEN. SYS ERROR.

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A POTENTIAL CONFLICT WAS OBSERVED AND I CALLED ZTL TO INSTRUCT THEM TO START ACR Y DOWN TO FL210 AND UNDER ACR X AT FL220. ZTL ADVISED UNABLE TO DO THIS. SUBSEQUENTLY I SUGGESTED ZTL TO STOP ACR X FL210 AND THEN START ACR Y DOWN TO FL220. ZTL THEN REPLIED; 'YOU ARE TALKING TO ACR X.' (DUE TO MY LACK OF TIME ON THE SECTOR I DID NOT REALIZE ACR X HAD JUST BEEN SWITCHED TO ZTL.) I REPLIED; 'OKAY; WE WILL STOP ACR X AT FL210 AND ZTL START ACR Y DOWN TO FL220.' PROBS AROSE WHEN I HUNG UP AND TRIED TO TALK TO RADAR MAN. RADAR MAN VERY BUSY AND MY LINES WERE ALSO RINGING. I ANSWERED MY LINE AND STARTED TO ISSUE A CLRNC TO ABY APCH CTL AND BROKE AWAY MOMENTARILY TO TELL THE RADAR MAN TO STOP ACR X AT FL210. THE RADAR MAN REPLIED; 'I SWITCHED THE ACFT TO ZTL.' IN RETROSPECT I SHOULD HAVE IMMEDIATELY CALLED ZTL BACK AND TOLD THEM THAT ACR X HAD ALREADY BEEN SWITCHED TO THEIR FREQ. DUE TO THE AMOUNT OF TIME REMAINING BTWN THE 2 ACFT CONFLICTING; I THOUGHT ACR X WOULD GO OVER TO ZTL AND CHK IN AND THEY WOULD STOP ACR X FL210. HOWEVER; ACR X DID NOT CHK IN UNTIL 3 MINS LATER; STATING CLBING TO FL220. ZTL CTLRS DID NOT HEAR THIS INITIAL CALL OR 2 MORE SUBSEQUENT CALLS. I HAD ONLY BEEN SIGNED ON THE SECTOR FOR A FEW MINS AND WAS TRYING TO GET A COMPLETE PICTURE OF WHAT WAS HAPPENING; AND AT THE SAME TIME; HANDLE SOME OF THE PROBS AND COORD THAT THE SECTOR WAS BURDENED WITH. NEITHER THE RADAR MAN NOR MYSELF ATTEMPTED TO CALL ZTL UNTIL WE NOTICED ACR X WAS CLBING THROUGH FL210 AND THEN IT TOOK SEVERAL ATTEMPTS TO GET THROUGH. ZTL FINALLY REPLIED; 'HE'S STARTING DOWN NOW.' APPARENTLY ZTL STILL DID NOT REALIZE THEY WERE TALKING TO ACR X CLBING TO FL220. SUPPLEMENTAL INFO FROM ACN 240844: ZJX CLRED ACR X TO FL220; ZJX HANDED US OFF TO ZTL. THE CTLR WAS BUSY BUT WE TRIED TO ESTABLISH COMS 4-6 TIMES. HE DID NOT RESPOND TO US BUT CONTINUED TO COMMUNICATE TO OTHER ACFT. ON OUR TCASII WE SAW ANOTHER ACFT DSNDING OUT OF FL230; HDG TOWARDS US. WE WERE OUT OF FL215. I HIT THE IDENT BUTTON ON THE XPONDER TO GET ATC ATTN. ON OUR OWN WE DSNDED BACK TO FL210 TO GET BELOW THE JET DSNDING TO FL220. AFTER WE DSNDED ON OUR OWN; ACR Y PASSED OVER HEAD BY 500 FT. I SAW THE ACFT VISUALLY 3 MI AHEAD. OUR TCASII HAD TA MODE ONLY. THEREFORE WE DID NOT RECEIVE AN RA ADVISORY. I FEEL IT WAS THE AWARENESS OF THE CREW AND THE TCASII THAT KEPT ACR X AND Y SEPARATED.