Account arrears not viable

I’ve been trying to to get hold of Vodacom cancellations department. I left messages, phoned numerously. Still no response. I went to a Vodacom shop to get assistance to cancel my contract. They told me I have an outstanding balance. They can’t tell me what my arrears is? They said that they can not cancel my account before I pay my arrears. According to my Vodacom app, It shows no outstanding balance. I have not received any data or airtime the last 3 months? How can I owe you money? Please cancel my contract and transfer my telephone number to pre paid