How to delete an unknown object?
The DBA_OBJECTS view describes all the objects in the database. In it, you can find, by instance, the name of an object, its owner or its type.

Example:

SELECT owner, object_name, object_type FROM dba_objects WHERE object_name = 'MY_OBJECT'; -- Be careful, the name is case sensitive.

OWNER               OBJECT_NAME         OBJECT_TYPE 
------------------- ------------------- -------------------
MY_USER             MY_OBJECT           PROCEDURE


Now, you can easily drop it:

DROP PROCEDURE MY_OBJECT;