Good ISP but got billed a year after I cancelled

As an ISP, RSAWeb is great and their home fibre service on Octotel I will highly recommend. However, almost a year after cancelling my service I randomly got a debit order that went off of my account for R999. That is a horrible, inexcusable rookie mistake and should never happen at a respectable business. I don't know what terrible process they use for billing but this kind of thing should never happen. Ever.