Your not alone ive done it before... :
Snap!
I once cleaned the wrong property three times in a row; every month.
The lady that asked me to quote seemed so nice, I was sure she would cough up end; even though I left an envelope after each clean.
Unfortunately I cleaned the wrong house each time and after the third time I received a phone call from some bloke who explained that he lived mostly in France; hence the delay in contacting me; and he didn't know who I was, or why I was cleaning his windows.
I honestly could've thumped him; 'cos I didn't/don't exactly believe him!