Incorrecting billing and handing over of account

Very very bad service, i took out a contract with them and cancellation was done the very next day as i could not cancel with my current subscriber, they handed me over to Authorities telling me I owe them +- R2500, when cancellation was done, i asked the lady if there are any monies due and her exact words to me was if it was only a sim card and it was not activate or used there is no bill. On communication they provide a whatsapp number to contact them, i did and the lady was just being absolutely rude. I ended up blocking her, i have asked for a detailed billing account as proof of what i used as the sim card is still sealed and was never used. I was never provided with it, i also requested a copy of the call where the lady advised me that there is no billing. i just received another sms over the weekend that they have handed me over to the credit bureau. Pathetic Pathetic customer service. i want the detailed billing account to show what data i used as well as the recording of the call where i was told that nothing is due.