Paid up letter not sent

My sister Thandeka Ndlangamandla has been owing Blue Label Connect and we called to find the balance. In October 2023 we organized for a debit order which Blue Label Connect debited. They were suppose to send us a paid up later and they did not. We have been calling and we were promised it will be sent within 72 hours but it was not sent. My sister is frustrated now, why such incompetence? Why do you not do this just small thing?