If you reach the confirmation screen, and receive a confirmation number, you can be sure your payment was completed. If you confirmed your payment in online banking, but did not get redirected to a confirmation page at the online retailer website, then there was a technical problem.
One of two things may have happened:
You can often determine that it was case (1.) if the online retailer sends you a confirmation email, or allows you to check your order history on their website. In case (2.), the funds will be (in most cases) re-credited to your bank account within minutes.
If you are uncertain, contact the online retailer to ask whether your order has been processed.