remove extension 300809@from-internal

failed to remove extension 300809@from-internal

sip show user   300809

* Name       : 300809


Secret       : <Set>
  MD5Secret    : <Not set>
  Context      : from-internal
  Language     :
  AMA flags    : Unknown
  CallingPres  : Presentation Allowed, Not Screened
  Call limit   : 0
  Callgroup    :
  Pickupgroup  :
  Callerid     : "device" <300809>
  ACL          : No
  Codec Order  : (ulaw|alaw)

/etc/asterisk/extensions.conf