As I undersood you are able to connect as internal.
So you can use DELETE command. I had the similar problem with corrupted object - I could not drop it and use it at all.
So are you ready to play with systems tables? If yes: shutdown your DB and make a full backup.
Everything very easy: you have to delete all informatiuon from DB about your Trigger based on object_id.
select object_id from dba_objects where object_name = 'YOUR_TRUGGER'

OBJECT_ID
36056

select column_name,table_name from dba_tab_columns where column_name = 'OBJECT_ID';

For example sys.ALL_PROBE_OBJECTS table contains the object_id ...

After that you have to check all tables which have that object_id and it could be another field name in different tables, probably you have to review views to extract table name ... and so on. At the and you will get around 20-30 records which have to be deleted from DB, after that, if everything was correct you will not see your TRIGGER any more in the database.

You can choose what is easyer for you?