Cant work 4th column in dependant select box - php

Question

I have csv with 4 columns. If i select make it shows models then year. I want it to show versions at the 4th box. however nothing happens. i have changed code and it will show versions in the 3rd box and then years disappears. still nothing in 4th box.
Played around with this bit of the code which makes the above effect but cant figure out why the 4th select box dont work.
$makes_models_years_versions = array();
$uploads_folder = wp_upload_dir()['basedir'];
$file = fopen($uploads_folder.'/make_model_year_version.csv', 'r');
$firstline = true;
while (($line = fgetcsv($file)) !== FALSE) {
if ($firstline){
$firstline = false;
continue;
}
$makes_models_years_versions[$line[0]][$line[1]][$line[2]][] = $line[3];
}
COMPLETE CODE BELOW:
function ajax_cf7_populate_values() {
// read the CSV file in the $makes_models_years_versions array
$makes_models_years_versions = array();
$uploads_folder = wp_upload_dir()['basedir'];
$file = fopen($uploads_folder.'/make_model_year_version.csv', 'r');
$firstline = true;
while (($line = fgetcsv($file)) !== FALSE) {
if ($firstline){
$firstline = false;
continue;
}
$makes_models_years_versions[$line[0]][$line[1]][$line[2]][] = $line[3];
}
fclose($file);
// setup the initial array that will be returned to the the client side script as a JSON object.
$return_array = array(
'makes' => array_keys($makes_models_years_versions),
'models' => array(),
'years' => array(),
'versions' => array(),
'current_make' => false,
'current_model' => false,
'current_year' => false
);
// collect the posted values from the submitted form
$make = key_exists('make', $_POST) ? $_POST['make'] : false;
$model = key_exists('model', $_POST) ? $_POST['model'] : false;
$year = key_exists('year', $_POST) ? $_POST['year'] : false;
$version = key_exists('version', $_POST) ? $_POST['version'] : false;
// populate the $return_array with the necessary values
if ($make) {
$return_array['current_make'] = $make;
$return_array['models'] = array_keys($makes_models_years_versions[$make]);
if ($model) {
$return_array['current_model'] = $model;
$return_array['years'] = $makes_models_years_versions[$make][$model];
if ($year) {
$return_array['current_year'] = $year;
$return_array['versions'] = $makes_models_years_versions[$make][$model][$year];
if ($version) {
$return_array['current_version'] = $version;
}
}
}
}
// encode the $return_array as a JSON object and echo it
echo json_encode($return_array);
wp_die();
}
// These action hooks are needed to tell WordPress that the cf7_populate_values() function needs to be called
// if a script is POSTing the action : 'cf7_populate_values'
add_action( 'wp_ajax_cf7_populate_values', 'ajax_cf7_populate_values' );
add_action( 'wp_ajax_nopriv_cf7_populate_values', 'ajax_cf7_populate_values' );