Lancet Labs Bloemfontein - Rude and Unprofessional

Today I was again reminded how rude and unprofessional people can be. I received an email today from Lancet Labs Bloemfontein for an outstanding amount. This was the first time I received any correspondence from them regarding any outstanding amount. I paid almost immediately. An hour or two later Lancet Labs phones me and the woman on the line rudely asks: So, when will you pay? I said that I already paid. Then she demands to know how much I paid. Not being able to remember the exact amount, she then continues stating: So, you can't provide proof of payment! I will NEVER again make use of their services.