Lack of customer service and problematic billing

In early July I had blood tests done at my doctor. I did not receive an invoice. What must have been more than a month later I got an SMS telling me my account was outstanding. I called the number included. Someone assured me than an invoice had been sent and promised to email it again. I received nothing. About a month later I got another SMS. Same thing. I called again. The same woman spoke to me. I should add that she had a terrible attitude. She said that she would email it. She then also said I must call head office to request it. I said I would not do that as it was their responsibility, and besides I had called the number given in the SMS. About two weeks ago I got another call. For the THIRD time I requested they send the invoice. I was assured it would be sent immediately. Lo and behold, I've still not received an invoice. I am quite disgusted by this service. Every time I interact with your staff they border on rude and I cannot understand how Lancet cannot get it right to send me the invoice. It is ridiculous. The amount is something pathetic like R150 but I cannot and will not pay without receiving an invoice. Kindly sort this out immediately please.