Call to undefined method App\Product::getProductStock()

BadMethodCallException Call to undefined method App\Product::getProductStock() This error occurred while accessing the model function in controller

My Controller

        $user_id = Auth::user()->id;
        $user_email = Auth::user()->email;


        // To prevent out of stock material from ordering
        $userCart=DB::table('cart')->where('user_email',$user_email)->get();
        // echo "<pre>"; print_r($userCart); die;
        foreach ($userCart as $cart) {

            $product_stock= Product:: getProductStock($cart->product_id,$cart->size);
            echo $product_stock;

            if ($product_stock==0) {
                return redirect('/cart')->with('flash_message_error','Product is Stock sold out. Buy another product');
            }

            if ($Cart->quantity>$product_stock) {
                return redirect('/cart')->with('flash_message_error','Reduced product stock & Try Again');
            }

        }

Model

public static function getProductStock($product_id,$product_size)
{
    $getProductStock=ProductsAttribute::select('stock')->where(['product_id'=>$product_id,'size'=>$product_size])->first();
    return $getProductStock->stock;
}

via Chebli Mohamed