A difficult one to figure out Mike, your prices are not unreasonably high by any means, broadly in line with my own prices although I deal in Euros whereas yours are Pound Sterling, but more or less near enough. Most of my customers are repeats, some going back twenty years and I gets loads of referrals all the time.
My advertising spend would be around £50 per week at most and I make no big effort to keep in touch with any of my customers, they just ring me when they need me again.
The only difference that I detect Mike is this, my customer base is largely rural, farmers,and small towns and villages whereas I think you live and operate in a large City with a higher concentration of opposition. But then on the other hand you must have a vast population of potential customers. But having said that you appear to me to be one of the most succesful cleaners on these boards so you are certainly doing something right.