Bad idea I think.
if you want to say about no increase this year say it without putting doubts in thier minds, or just dont say anything. as just said offering a customer an incentive to recommend really does work well and mention your website then do that in a letter why stir up peoples feeling when you are trying to be nice. Maybe try something like this.
Dear ******
I would like to thank you for your custom and let you know about a few changes that have been made by me/us.
there will be no price increase this year.
We have a new website to contact us if you need too for any reason. recommend a freind and we give you £* off your next bill if you get freinds to visit out website and book a regular clean ask them to give your address as a reference and we will discount on the next clean we do for you.
Thank you for your custom we/I appreicate it.
Kind regards
*************
Thats only rough but can you see the points they are good ones and do not start off badly.
Hope that helps a little.
And Chin up we all have bad days tomorrow is a new day and may it be great for all of us
Ian