INFLT ICING. UNABLE TO MAINTAIN ALT.

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LEVEL AT 17000 FT WBOUND (LOW ALT SETTING) ADVISED ATC I WAS PICKING UP SEVERE ICE AND NEEDED FL190. ATC ADVISED HE WOULD LET ME KNOW. AFTER SEVERAL ATTEMPTS (3 MINS) I INFORMED THE FREQ 128.65 THAT I WAS CLBING TO FL190. BY THIS TIME THE AIRSPD HAD DETERIORATED FROM 195 KIAS; TO 160 KIAS (THE MINIMUM RECOMMENDED IAS FOR CLB IN ICE). I ATTEMPTED A STEP CLB TO FL190; HOWEVER; I COULD GET TO ONLY FL180. (STILL NO RESPONSE FROM ATC.) IT BECAME OBVIOUS I WOULD NOT BE ABLE TO MAINTAIN FL180; SO I REQUESTED 16000 FT; NO RESPONSE. I INITIATED A DSCNT TO 16000 FT. AFTER AGAIN INFORMING THE FREQ 128.65 ON MY WAY DOWN I GOT HOLD OF ATC AND HE CLRED ME TO 16000 FT; INFORMING ME THERE WAS SOME CONFUSION ON WHO WAS TAKING WHICH SECTOR (CTLRS) DURING THEIR AM SHIFT CHANGE. PRIOR TO REACHING RED TABLE I INFORMED ATC UNABLE TO MAINTAIN 16000 FT REQUESTED 14000 FT. ATC ADVISED THE MEA DID NOT ALLOW BELOW 16000 FT FOR A FEW MORE MINS. I WAS UNABLE TO KEEP 16000 FT; AND ALLOWED THE ACFT TO DRIFT TO 15000 FT. I THEN RECEIVED A CLRNC TO 14000 FT; THEN BECAME VFR. ALL OF THE ACFT ANTI-ICE AND DEICE WERE OPERATING CORRECTLY. I ATTRIBUTE THE PROB TO: ATC WAS FOCUSED ON THEIR PROBS IN HOUSE; I DID NOT TAKE EMER ACTION FAST ENOUGH AFTER IT BECAME CLR ATC WAS NOT AWARE OF MY PROBS; ACFT PERFORMANCE WAS AFFECTED BY AIRFRAME ICE; BELLY AND CUP OF WING.