Really poor service

I cancelled our contract as you cannot call anyone only whatsapp. They never mailed the cancellation fee invoice, but did collect router which they mislaid, I was handed over to their legal department, I sent POP and all whatapp chats, and proof they had collected router. Yesterday I recieved a whatsapp demanding R999. This is unacceptable, I waited at least 20 minutes before I was assisted. It takes them 72 hours to allocate a credit note. I wont even go into during the time we were with them how many times the line dropped and poor assistance.