They became bad payers 9 years ago,  you don't really like them, but decided to give them another chance, Fair dues,
  but it looks like History is repeating itself,   i would just write the measly £7.50 Off they are messing you about for, 
  its not worth your time to be worrying about selfish neighbours like these for £7.50,  just sack them off, never ever
  clean for them again.