Golf gti left rear door locking system

it is probably your door lock has gone into safe mode.you need a new door lock.try using the lock/unlock button on your remote or on the drivers door button and gently tap the door handle with your hand while pressing the lock/unlock button,carefull not to dent your car.if that does not work,try disconnecting the cars battery for a few minutes,but note the vehicle might pick up fault codes which need a diagnostic machine to clear...good luck