Harassed over a paid account

In May 2014, I was contacted by this company for an outstanding City of Johannesburg Municipality account. This was my first (and only) property I'd ever bought, and I had no idea how this all worked. I also wasn't receiving the statements, so was shocked to find out I owed about R14000. As I knew I was liable for this, and I was lucky enough to be in a position to settle the account, the account was paid straight away. I dealt with Dean Saunders, who was very helpful. He opened a new account for me, which I've been paying for the last 18 months. Over the last year and a half, I have been contacted by this company twice to advise me that it's outstanding, and I've been handed over. This is bordering on harassment, for an account that was settled in full as soon as I was aware of it. Update your systems and leave me alone, or I will be looking into suing you for harassment.