get over yourself mate!customers often forget what day it is never mind how much they owe you!
little tip for you
always write the date you cleaned them on your ticket and be gracious and polite when they get mixed up with how many cleans they owe you.
oh and never go collecting on a sunday.it looks a bit desperate and sad.unless of course you are!!

hope your also not the sort of window cleaner thats gets annoyed if he doesnt get every single penny in thats owed to you every week as it simply wont happen!!
debt is part of running a business!
regards
dazmond