Easy Clean,
My advice is to continue cleaning your "underpriced" customers until the 1 year anniversary date then increase the prices. Meanwhile, continue to canvass and make sure you quote a more realistic price for any new work you get.
The reson I would not increase your prices now is because you have only had them a few months and you're already asking for more!! It's not their fault you underpriced. I would wait and increase year on year in line with inflation. People will accept an annual increase more than a 4 month increase, they will be worried when the next one is due!
best wishes,
Trev