Finance department horrible experience

So I am new parent at Sparks and the school is amazing, the kids are loving school. The admin head office, finance side is like another company. I paid registration fee and school fees but still not reflecting on my account. This was done from Sep 2019 - Feb 2020 and I am still getting wrong, receive the invoice that is wrong still.

For past month and a half I have been requesting a simple letter stating I am liable for the fees for work purpose. I called today and was promised the letter within an hour and its been almost 2 hours. This is required by work and a month and half still no action. I need this letter today