class Index extends MagentoFrameworkAppActionAction
{
protected $resultPageFactory;
protected $session;
private $productRepository;
public function __construct(
    FormKey $formKey,
    Cart $cart,
    Product $product,
    MagentoFrameworkAppActionContext $context,
    MagentoCustomerModelSession $customerSession,
    MagentoCatalogApiProductRepositoryInterface $productRepository,
    PageFactory $resultPageFactory
)
{
    $this->session = $customerSession;
    $this->formKey = $formKey;
    $this->cart = $cart;
    $this->productRepository = $productRepository;
    $this->product = $product;
    parent::__construct($context);
    $this->resultPageFactory = $resultPageFactory;
}
public function execute()
{
    if (!$this->session->isLoggedIn())
    {
        $resultRedirect = $this->resultRedirectFactory->create();
        $resultRedirect->setPath('customer/account/login');
        return $resultRedirect;
    }
    else
    {
        $resultPage = $this->resultPageFactory->create();
        $resultPage->getConfig()->getTitle()->set(__('My Wallet'));
        $sku = '';

        $vat_exempt_name = $this->getRequest()->getPost('vat_exempt_name');
         //...........Load Product...............//
        $product= $this->loadMyProduct();
        $ID = $product->getId();

    //.............. For Add to Cart .........//
    $productId =$ID;
    $params = array(
                'form_key' => $this->formKey->getFormKey(),
                'product' => $productId,
                'qty'   =>1
            );
        $product = $this->product->load($productId);
        $this->cart->addProduct($product, $params);
        $this->cart->save();
        return $resultPage;
    }
}
    public function loadMyProduct()
    {
        if (empty($sku)){
        $this->createProduct();
        }
        else{
        return $this->productRepository->get($sku);
        }
    }
    public function createProduct(){
        $posted = $this->getRequest()->getParam('vat_exempt_name');
        $objectManager = MagentoFrameworkAppObjectManager::getInstance(); // instance of object manager
        $product = $objectManager->create('MagentoCatalogModelProduct');
        $product->setSku('my-sku44'); // I need this SKU to be set for global variable $sku
        $product->setName('Wallet Amount'); // Name of Product
        $product->setAttributeSetId(4); // Attribute set id
        $product->setStatus(1); // Status on product enabled/ disabled 1/0
        $product->setWebsiteIds(array(1));
        $product->setWeight(10); // weight of product
        $product->setVisibility(4); // visibilty of product (catalog / search / catalog, search / Not visible individually)
        $product->setTaxClassId(0); // Tax class id
        $product->setTypeId('simple'); // type of product (simple/virtual/downloadable/configurable)
        $product->setPrice(199); // price of product
        $product->setStockData(
                 array(
                      'use_config_manage_stock' => 0,
                      'manage_stock' => 1,
                      'is_in_stock' => 1,
                      'qty' => 99999
                      )
                     );
        $product = $product->save();
        $ID = $product->getId();
        //global $sku;
        $sku = 'my-sku45'; // here global variable $sku should update
    }

}