A complaint lands in a queue, in front of a person with a script and limited authority. Knowing what that person can and cannot do changes how you write it.
Most questions families get stuck on about school have a person whose actual job is answering them. The difficulty is knowing which person, and how to ask.
The last quarter is when the people who owe you money start managing their cash instead of yours. Here is the order to work through when an invoice slips.