20 years a subscriber and threatened by Sharetrackin

I has been a subscriber to this service provider from 1995/96. Due to the current bad economic situation, I made a request on the company's website, on their 'contact us' tab, during November 1999, that I would like to cancel my subscription. Nobody contacted me to offer assistance nor explain to me what I need to do to cancel my subscription. The debit orders kept on going off. During February 2020 I made the same request on their website to contact me. Nothing happened and the March debit order was again honored. I stopped the debit order and suddenly in November 2020 I was contacted with the message that my subscription is in arears. I told the lady that I did give notice on their website. She told me that I need to fill in a cancellation form before I can cancel. This requirement is not in the terms of condition. I submitted the form and agreed that I will made a final payment of R500. Now they are threatening me that if I don't make a final payment they will take steps. I think for a loyal customer for over 20 years, this treatment is unfair.