charge enough to make it worth your while , dont worry about others.
The price of living has gone up true, but has people wages or disposable income ?
It has to be a happy medium, window cleaning is not an essential service.
Sounds like you could increase a bit though £10 / £12 ?, if you have a long standing and loyal customer base explain this rise in the fact your prices have not risen since starting and this is to reflect your running costs.
I am charging more to new customers now and trying to increase the lower priced ones slowly and by a small amount to offset any I may lose, especially over this winter.
Simon