Hi,
If you set a return URL in a payment plugin, you should go to that URL after the paiement.
If you don't, then you'll be redirected to the defaul thank you page of HikaShop at index.php?option=com_hikashop&ctrl=checkout&task=end
The exact URL will be different because of the SEF.
If you get the URL "component/hikashop/product/listing" and you don't remember adding that URL anywhere, then it's probably that you entered the URL of the checkout or of the cart display as return URL. But since after the payment the cart is emptied, HikaShop can't display these pages and will automatically redirect to the URL you set in the option "URL where you will be redirected when the cart is empty" or to the page "component/hikashop/product/listing" if you didn't set any URL in that option.
So please check that.