You can call the stored procedure using this statement in the PL/SQL block.Just make sure the function to which you are going to call is exist or not.If it doesn't exist in the database catalog then you need to create it first with the name specified and include the name with the EXECUTE IMMEDIATE statement.
To call a procedure using EXECUTE IMMEDIATE,you can use this code -
2 Result VARCHAR2(60);
4 EXECUTE IMMEDIATE Proc1('[optional_arguments]');
5 EXECUTE IMMEDIATE Proc1 ('[optional_arguments]') INTO :Result
6 USING OUT Result;