Poor service

I have had the contract with MTN which expired in May 2020 and i have been trying to cancel the contract with no success from the retention department. Sometimes i hold for more than 2 hours or sometimes when they it will be like the network issue and they hung up my phone.I dont receive their invoices which i call MTN to tell me how much I owe to them and they will say R109. Now they say I owe them R448 of which is more than what are used to pay. How do you operate MTN. Can someone assist i cannot be billed for something that i dont know. This is **************** that you are doing.