I think you can say you are not paying until you see the order receipt and certification for the window to ensure compliance and what was paid for that. You should then ask that the rest of the works be broken down so that you have an invoice which is a mini schedule of works i.e.
1. Remove...
Firstly, under no circumstances continue any further work with this person. Regardless of the urgency of works required, a written quotation with terms and conditions such as payment terms always needs to be established. He simply cannot demand payment in such a short time frame.
You also need...