If you need order support, to manage your order, subscription, invoice and payment details, please open this web page https://store.nero.com/myaccount/ and sign/login using your email address which used when bought the order. 

Below is an example of Product/subscription information of an order. In the bottom part, there is also information about how to get support.

After login, you will see below screen. You could view details of your each order, get invoice, manage your subscription and payment method there.