Ackermans payment not found

I have an account with Ackermans and in the 3 Jan I settled the balance at Refinery, I have been getting messages from Ackermans since the day I paid that the payment is still due. I have spoken to consultants who are now telling me I must go in store to ask for a receipt. Why am I the one being inconvenienced?? This is frustrating because it will reflect badly on my credit record.