OK, update time!
First of all, thanks Sander. I understand that everyone has other things also in their lives to attend too.
I have indeed been contacted on Monday the 6th of October that they will look into the issue. Several replies later, they had found the money "hidden" somewhere in their system. On October 7, I have received a tracking number from DHL for my shipment.
Now, I am not saying that everyone will have problems when ordering. The point of this post was to inform other people what I have been through. Experiences will vary, and this is mine. The end result is that this will be my final purchase from the Ultimaker store. I may receive the order finally, but the handling of the case in the start was a jarring experience.
The first replies have been late and dismissive (there is no excuse that the money were without a reference number, and that is the reason they didn't find them. I have contacted them BECAUSE there was no reference number!!!. Surely, no one has money deposited on their account and doesn't know it!).
Only after informing Ultimaker that I contacted a Dutch customer protection agency and the Police (on Saturday, the 4th Of October) things have changed. The handler of my case was changed, replies have been swift and frequent, and a solution was given. And I really regret having to resort to such lengths!
Am I satisfied? No... Will I order again? certainly NOT. UNLESS, I see in the front page of Ultimaker.com an announcement that they acknowledge the crappy payment system, that they will fix it, and that they will make (not try to make) the customer service a real service and not a waiting queue, as a "thank you" to all the people that have made them what they are now.
Again, many thanks to Sander, Maritt, and the people that posted on this board their experience. I am done with Ultimaker...