Lancet - Harassment by call centre

Receive an invoice for an outstanding amount of less than R200. 3 working days later I get a call from their collections department. 2.5 hours later I get another call. I'm a long-standing client of Lancet, and always pay, so why are they making me feel like I'm going to be blacklisted. I also don't want to have to follow a whole bunch of security questions, which once again, is a total waste of my time. I will be taking my business to Ampath in the future.