Rückgabe String aus Subroutine geht nicht !

@ECHO off 
SETLOCAL

SET "searchstring1='CONTACT_FORMAT_GREETING_COMMON',"  
SET "searchstring2=CONTACT_FORMAT_GREETING_MR',"  
SET "linestart=START"  

FOR /f "delims=" %%i IN (inputfile.txt) DO (  
	SET "textline=%%i"  
	SETLOCAL enabledelayedexpansion
	if "!textline!" neq "!textline:%searchstring1%=!" (  
		CALL :findString "!textline!" %searchstring1% %linestart%  
		echo !linestart!
		REM Write the modified line
		) ELSE (
		REM Write the unmodified line
		)
	if "!textline!" neq "!textline:%searchstring2%=!" (  
		CALL :findString "!textline!" %searchstring2% %linestart%  
		echo !linestart!	
		REM Write the modified line
		) ELSE (
		REM Write the unmodified line
		)
	ENDLOCAL
)
GOTO :ENDE

:findString -- returns position of first occurrence of a string in another string

SETLOCAL ENABLEDELAYEDEXPANSION
set "mainstring=%1"  
set "substring=%2"  

Set "rest=!mainstring:*%substring%=!"  
echo Rest: %rest%

Set "anfang=!mainstring:%rest%=!"  
echo Anfang: %anfang%

ENDLOCAL &set "%3=!anfang!"  
GOTO :EOF

:ENDE
ECHO Done^^!