Oracle 12, i do impdp

Hello gurus,

     1 - I am in version 12.1.0.2

          When i do an impdp i have this next error : ORA-39346: data loss in character set conversion for object DATABASE_EXPORT/SCHEMA/TABLE/STATISTICS/TABLE_STATISTICS

     2 - I would like Delete all my statistics, and statistics system.

          2-1 delete all my statistics ( All schema ) and statistics system.dbms_stats.delete_schema_stats('NOM_SCHEMA'). Correct ?

          2-2 Recreate all my statistics ( all schema, and system )

          But i have plenty of schema how is it possible drop all the statistics of the schema.

          BEGIN

             DBMS_STATS.GATHER_TABLE_STATS (

                    ownname => upper('$SCHEMA_NAME'),

                    cascade => $CASCD,