Paid up letter

I have been calling them since morning payment was made on the 30th April 2019 and they can see the money that was paid and POP was e-mailed to them same time after payment was made but they don't want to give me a paid up letter which is holding me back with important things that I need to do.

Dikeledi refused for me to talk to her manager or supervisor, even after informing them that I need this letter before 12pm they wont assist me.