I'm sorry to hear you lost your good/biggest job squeaks.
I do a big old georgian one and it comes up well(to my surprised relief), as do any old leaded that i have done. I've had my share of disasters and complaints though.
From your post you seem to deal with the housekeeper, and not the actual householder.
I believe that you have a perfect right to get mr or mr's actress on the phone and say that you have been cleaning their windows for twenty years both as an employee of someone else , and on your own behalf. You could point out that you have given good service, been honest, and discreet over this period. You deserve a bit more than an answer phone message.
I think you've got an excellent chance of getting this back if you can bypass the housekeeper.
As regards what Matt says, yes your van should be signwriten but if you haven't got the money that can't be helped. Mines brilliant , fantastic, but it hasn't got me any work yet. In theory though it should and I think you agree with that.
I always get the sence with you squeaky that you rubbish WFP, If you go around telling people (the housekeeper for instance) that it's crap then you can't expect them to be supportive.