Unacceptable business practices

I work at a school and we cancelled our services with Vox since we moved over to a local fibre supplier. Now we followed the procedure by sending a cancellation email and received a response stating that they received the request. This all was in May 2019. We are still getting billed. This was only picked up by a new finance officer. I've tried to phone and get some form of response from Vox with no joy. Numerous calls were transferred to another department and then dropped. This is thousands of rands wasted that could have gone to help our kids.