Would I be right in thinking that you are not accustomed to dealing with customers of this type.
They have their processes and there is no point in raging against that.
You sent them an invoice, but was it done their way, did you quote their purchase order, their job number etc.
You need to learn how they work and conform to that way of working, they are not going to do things your way after all.
Get on to their accounts payable and ask what you need to do to get paid, it may be quite a complicated process especially if you are a new supplier. Jump through all the hoops.
The idea of holding back on job 2 until you get paid for job one, or as another poster says escalating things in 24/48 hours, is just the wrong mindset for working with a large bureaucratic company.
They have come to you twice in 3 months, they must like your work, this could be an opportunity, don't blow it just because they are highhanded in their financial dealings.
Next time the come calling you can pour all your frustration into charging them at a much higher rate than your usual, that is also part of the mindset required dealing with big companies.
You said, "its not the money, its the principal of the thing". I suggest that there is no principal involved just a different way of operating and if you can get your head around it perhaps a very profitable one.