Internet order placed but no order acknowledgment

I have placed an Internet order for an XPS 15 on 8 April 2017. I have received an "acknowledgment of receipt of your Dell Order". This has an "Internet Receipt Number".

I have not heard anything since. I have tried to contact support, but in each case I need an Order Number, which, of course I do not have, since I have not received an "order confirmation".

I am unable to find a way to contact Dell without providing an order number, but since I don't have an order number I am trapped!

Please can you help me to progress this order. Ideally I need a way of contacting Dell which does NOT require an order number, but I cannot find how to do this.