Cache API Calls - php

Question

I have following code to call and echo some API calls from a site.
function popular_uploads() {
// If no saved data exists in the cache
if ($json_data === false) {
// Fetch new data from remote URL
$gameid = $instance['code1'];
$url = ("http://thegamesdb.net/api/GetGame.php?id=".$gameid."");
$json = file_get_contents($url);
$json_data = json_decode($json, false);
set_transient('my_unique_identifier', $json_data, 3600); $json_data = get_transient('my_unique_identifier');
}
foreach ( $json_data->items as $item ) {
$title=$item->Game->GameTitle;
$boxartw=$item->Game->Images->boxart[0];
$boxart=$item->Game->Images->boxart[1];
if ($boxart == NULL) {
$boxart = $boxartw;}
$publisher=$item->Game->Publisher;
$releasedate=$item->Game->ReleaseDate;
$newdate = date("d/m/Y", strtotime($releasedate));
$newday = date("d", strtotime($releasedate));
$newmon = date("m", strtotime($releasedate));
$newyear = date("Y", strtotime($releasedate));
echo '<div class="upcoming_games_side">';
echo '<div class="upcomig_bg"style="background-image:url(http://thegamesdb.net/banners/_gameviewcache/' .$boxart. ');></div>';
echo '<div class="dark-screen-uc"></div>';
echo '<img class="game-boxart_uc" alt="" src="http://thegamesdb.net/banners/_gameviewcache/'.$boxart.'"/>';
if ($title == null){
echo "N/A"; }else{
echo '<h1 class="title_uc">'.$title.'</h1>';}
if ($publisher == null){
echo "N/A"; }else{
echo '<p class="pub_uc">'.$publisher.'</p>';
}
if ($newdate == "01-01-1970"){
echo "N/A";
}else{
echo '<date class="date_uc">'.$newdate.'</date>';
}
$target = mktime(0, 0, 0, $newday, $newmon, $newyear) ;
$today = time () ;
$difference =($target-$today) ;
$days =(int) ($difference/86400) ;
if ($days == "0"){
echo "N/A"; }else{
echo '<date class="count_uc">'.$days.'</date>';}
echo '</div>';
}
}
But it's not working and doesn't Cache API data. So Where is my mistake and wahts part's of my code's are Wrong? I'd appreciate any help.
By the way, it's a Wordpress plugin.