Sorry to hear you’re having problems buying Dorico, Sjoerd. The End of Summer Sale does not include educational products, I’m afraid, so the educational crossgrade is not eligible for the sale discount, but it’s already very keenly priced.
Normally when there’s a problem with the verification process, it’s because of a change of some kind between when you submitted the verification request and when you come to resume your purchase: if you’re using a different device (e.g. now you’re on your phone, when you started on your computer) or you’re using a different browser, or you’re in a different geographic location. You may find that you need to start the process again, and make sure you can complete the process on the same device in the same location.
Please do open a ticket with the AskNet team – you should be able to enter “No order number” into the required order number field.
If in the meantime you need a time-limited license so that you can continue using Dorico while this is sorted out, please let me know.