ALTDEV ALT EXCURSION ON TCASII RA. POSSIBLE PHANTOM EVENT.

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WHILE CRUISING AT FL280; ABOUT 15 MI NE OF THE ISO VOR ON J121 A TA ALERT SHOWED UP ON THE TCASII FOLLOWED QUICKLY BY A RA ALERT. WE WERE IN THE CLOUDS. THE TCASII SHOWED TFC AT OUR 12:30-1 O'CLOCK POS AT OUR ALT. WE FOLLOWED THE TCASII INSTRUCTIONS TO DSND AT 2000 FPM. AT THIS TIME WE ADVISED ATC THAT WE WERE DSNDING BECAUSE OF AN RA. BTWN 27500 AND 27000 FT WE WERE GIVEN THE CLR OF CONFLICT BY THE TCASII AND INITIATED A CLB BACK TO FL280. DURING THIS PERIOD WE REPEATED OUR DEV AND THE REASON FOR THE DEV WHEN WE THOUGHT ATC DID NOT HEAR US WHEN WE WERE APCHING FL280 -- ATC ASKED US TO CONFIRM OUR ALT. WE ONCE AGAIN EXPLAINED WE HAD AN RA ON THE TCASII; AGAIN ATC DID NOT RESPOND. WE CALLED ATC AGAIN TO MAKE IT CLR THAT WE WERE RESPONDING TO AN RA. WE WERE TOLD TO STAND BY. ABOUT 5 MINS LATER HE CAME BACK TO US; WE EXPLAINED ONCE AGAIN; HE TOLD US THERE WAS NO TFC IN THE AREA. THIS WAS 10 MINS AFTER THE RA. I DON'T KNOW IF HE MEANT NOW OR THEN. WE WERE IN THE CLOUDS WITH ZERO VISIBILITY. WE HAD NO OTHER OPTION. I DON'T KNOW IF IT WAS AN ANOMALY OF THE TCASII. I DON'T KNOW IF THERE REALLY WAS A CONFLICT OR NOT. I DO KNOW THAT AFTER LEAVING MY ALT AND TRYING TO EXPLAIN TO ATC THAT WE HAD AN RA THAT THEY DIDN'T QUITE UNDERSTAND THE SIT OR WEREN'T AWARE OF WHAT A RA IS. THE LACK OF UNDERSTANDING OR COM WAS THE MOST DISCONCERTING ABOUT THE RA.