Katakana Character not loaded

Hi,

I am using oracle 11g database. one of my upstream send us feed with Katakana character in it. hence we are not able to load the data that contain Katakana character in oracle database table. I have already viewed some reviews & discussion in this website. I tried changing the column data type as NVARCHAR2. but still I Coudnt able to load the that Katakana character into table. Could some please help me to load the special(Katakana Character) into oracle database table.  is any other way to resolve this?