False advertising and billing ****

A few years ago, I subscribed to Rain to avoid being locked into a contract like other South African internet providers. This month-to-month arrangement suited me well, as they would disconnect my service if I missed a payment and reconnect it once I paid. In November 2024, I decided not to pay, and my service was disconnected. However, they sent me a bill claiming I owed them money, which I initially thought was a prank and ignored. In December 2024, they sent another bill, and in January 2025, yet another, with the amount continuing to increase. Their customer service has been unhelpful, with no one answering my calls and the chatbot offering no real solutions. I canceled the service this morning, but they told me I would still be billed even though my service was disconnected. How is this possible if I never signed a contract?