Remove Duplicate lines through RegExp

#include <Array.au3>
#include <File.au3>
Dim $aArray
$opentxt = FileOpenDialog('Choose TXT', @DesktopDir, '(*.txt)', 1, '')
$aRegExp = StringRegExp(FileRead($opentxt), "[0-9]{6,12}", 3)
$startmount = Ubound($aRegExp) ;<<<<<Maybe get wrong from here
_FileReadToArray($opentxt, $aArray)
_ArrayDelete($aArray, 0)
$newfile = _ArrayUnique($aArray)
$outputtxt = FileOpen($opentxt, 2)
_FileWriteFromArray($outputtxt, $newfile, 1)
FileClose($opentxt)
$sRegExp = StringRegExp(FileRead($opentxt), "[0-9]{6,12}", 3)
$endmount = Ubound($sRegExp) ;<<<<<And here
MsgBox(0, "Mount", "Before: " &$startmount  &@CRLF &"After: " &$endmount  &@CRLF &"Total Deplicate: " &($startmount - $endmount))