I am sorry to hear you're unhappy with the late payment fees and the confusion over how they are charged. Let me help you with this.
Late payment fees are only charged when the old bill is outstanding at the time of the new bill being created.
For example: if August's bill is not paid in full by the creation date of September's bill, this new bill will have a late payment fee added. This is fully in line with our terms and conditions, which you can see here