Nel,
I've recently had exactly the same.
Don't waste your time. Don't phone him. He's a 'lost customer'.
If you phone him now; he's pre-warned he's lost his window cleaner and will go looking for another before his windows get too dirty.
Just wait for his phone call, agree to clean his windows; give him a date if you like; and don't turn up.
Mess him about a bit!
If he collars you to complain, just explain that your priority is to provide a top service to your regular customers; and he's not one of them.
I've recently wound-up a rude customer who did similar and never did get round to doing her windows, despite her being desperate to get them done.
I had told her I'd do them the next time I was in the area, but didn't; then around two months later she saw me, give me a big smile (she never usually; just the opposite) and asked if I was doing her windows today. I smiled back and said, 'Not this month' (which is what she told Wor Lass some months prior).
She turned smartly to the right and marched off in the huff.
Lo and behold, I saw a 'for sale' sign outside her house last week!
Now I know why she wanted me so badly.
I really dislike these sort of people. It just seems so 'sneaky' and 'urine extracting' when they try to change the terms and conditions on you.
Drop 'em.