Parent questions her bill EVERY month

[Saltire]

I do a detailed bill listing every single day and the charges ( most of the time it is the samedaily charge) however this month i've had a lot of extra hours. All are listed in my attendance records that she's signed, in ym diary and on my calendar.
Getting a bit sick it now, all the looks as she pores over it

this is why i invoice in advance.

the parents know what hours they have booked and if they don't use them, they still have to pay for them

Any extra hours that are requested are to be paid at least 48 hours in advance.

Saltire, make yourself unavailable for extra hours and charge contracted fees regardless of whether or not the child has been there