Your #submit is an array you have put is as string, So change your submit entry to the following. and place $form['submit'] to $form['actions']['submit'];
$form['actions']['submit']=array(
'#type' => 'submit',
'#value' => t('Submit'),
'#submit' => array('complaint_form_submit'),
);
Note: **'#submit' is an array**
to add validations
$form['#validate'][] = 'complaint_form_validate';
Note: '#validate' is an array