Falling to cancel rain service

I have been trying to cancelling the service since last year May 2023 and I'm still getting invoices for a service I'm not using. I have been calling every month since then and all I get is that their cancellation service is offline. I always get a reference number and I'm told someone will get in touch and nobody does until to date. My router is always saying no internet connection, and I will make the monthly payment as I will receive the payment notification. However, I have stopped the payment and they called on 20 May 2024 to requesting for it. It is really frustrating to pay for a service and no one assist when you have problems. I have to buy data for my phone because there is no internet connection.