ZTL CTLR EXPERIENCED FREQ CONGESTION AND ISSUED INCORRECT ROUTING TO IFR ACFT.

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ACFT X CALLED FOR CLRNC ON 125.15; THE REGULAR ATC FREQ AT ZTL SECTOR 48. SECTOR 48 WAS COMBINED WITH SECTORS 45 AND 46 SO 3 FREQS WERE IN USE. THE INITIAL XMISSION WAS UNREADABLE. AFTER THE SECOND XMISSION I ADVISED ACFT X TO STANDBY. I TRIED TO COMPLETE ALL THE TASKS PENDING SO I COULD TALK TO ACFT X WITHOUT INTERRUPTION BY THE OTHER FREQS. I CLRED ACFT X TO 'PAWALKIE' VIA 'HOLSTON MOUNTAIN 180 AT 11' (HMV180011) 'AS FILED.' ACFT X READBACK WAS BLOCKED BY ANOTHER FREQ AND I HAD HIM READ IT BACK AGAIN. ACFT X DEPARTED AT XA57Z AND I CLBED HIM TO 10000 FT. WHEN I WENT TO SWITCH HIM ABOUT 1 MIN LATER I NOTICED HE WAS SBOUND. I ASKED HIM WHERE HE WAS GOING AND GOT A RTE DISPLAY. HE WAS GOING TO THE BARRETTS MOUNTAIN 1800 AT 11 (BZM 1800 AT 11). THE RTE DISPLAY SHOWED ALMOST DUE WBOUND. IT DAWNED ON ME THAT PWA WASN'T PALWALKIE IT WAS WILEY POST IN OKLAHOMA. I VERIFIED HIS DEST WAS WILEY POST AND CLRED HIM TO THE NEXT FIX ON HIS RTE OF FLT -- SOT360028 (SNOWBIRD) HE QUESTIONED THAT FIX AND I REPEATED THE CLRNC. HE TOOK IT AND I SWITCHED HIM TO THE NEXT SECTOR. HE WAS LAST SEEN HDG DUE N. FORTUNATELY THERE WASN'T ANY TFC IN THE VICINITY. THE NEXT SECTOR CLRED HIM DIRECT WILEY POST AND PUT IN THE LATITUDE/LONGITUDE FOR WILEY POST SO THE FLT PLAN WOULD PROCESS.