The company is Thomas Higgins.
Before you do though, have you been in of an evening, say 15 minutes before they open on a Friday night. Casually, but firmly, just say 'hi, I'm the window cleaner, just come to square up my bill'.
In my experience it happens with restaurants (especially the Indian kind) that it just gets put by rather than maliciously not paid.
If they ask you to wait, play it cool, order a beer-just wait.
Chances are they will pay, even if they bin you with it. Because they may run the risk of false telephone orders-could cost them much more than their window cleaning bill.
Whatever you do-play it cool.