[batch-file] windows batch file rename

I rename in code

echo off

setlocal EnableDelayedExpansion

for %%a in (*.txt) do (
    REM echo %%a
    set x=%%a
    set mes=!x:~17,3!

    if !mes!==JAN (
        set mes=01
    )

    if !mes!==ENE (
        set mes=01
    )

    if !mes!==FEB (
        set mes=02
    )

    if !mes!==MAR (
        set mes=03
    )

    if !mes!==APR (
        set mes=04
    )

    if !mes!==MAY (
        set mes=05
    )

    if !mes!==JUN (
        set mes=06
    )

    if !mes!==JUL (
        set mes=07
    )

    if !mes!==AUG (
        set mes=08
    )

    if !mes!==SEP (
        set mes=09
    )

    if !mes!==OCT (
        set mes=10
    )

    if !mes!==NOV (
        set mes=11
    )

    if !mes!==DEC (
        set mes=12
    )

    ren %%a !x:~20,4!!mes!!x:~15,2!.txt 

    echo !x:~20,4!!mes!!x:~15,2!.txt 

)