I got a new customer about 3 months ago. Similar thing. She gave me her number so i could text her the following month. Which i did 4 weeks later, only to be told that they were still clean and didn't need cleaning(but please don't forget me next month" her words. Sooooo, given her one more chance i text her a month later only for her to say that it looks like it might rain the next day or so, so please don't clean. But don't forget me next month(her words again) I was due back down her road today and guess what i forgot to do last night?
? Text her. What do these morans take us for? She's been dropped from such a height, only her dental records might giver her identity away. Can't wait for "that" call asking when i'm due round again 
I'll just have to say that i can't do them this month, BUT don't forget to text me next month The daft thing is she said that she's been looking out for a decent window cleaner for ages. Then she finds one, then she loses me just like that. Hey Ho 
Its seems there are people like this everywhere.
I have the same in a round i do. Thing is i could say im one of the cheapest WC's there is around this particular estate (as i live very close to it), im not doing theirs anymore, as im fed up being turned away - unless they phone me, and i'll tell them my prices have gone up.
The rest of the round are lovely people, and always give a bit more that what i charge.