Being billed for data I dont want and have not used because of misinformation from MTN employees

MTN does not even deserve 1 star. They are the worst service provider. On 10 August I phoned in to cancel my modem contract and had to hold the phone for almost 2 hours on which I then gave up. On 12 August I tried again and was put on hold for 1 hour and 10 min until I got through, only to be told that I had to phone back on 14 August because the contract expires on 13 August. I was also adviced to rather convert the number to a prepaid in order to avoid being billed in September. This meant 20 August would be my last debit order. When I phoned in this morning on 14 August, I was told that I will be billed for August and September because my invoice was closed on 12 August and I received the data. The data has not been used yet so I asked them if they could take it back so that I dont get billed in September. I was told they cant do that. I then asked if this meant that if I cancel it now I will forfeit the data. They said yes but I will still be billed in September even if I dont use or forfeit the data. I was then told to finish the data before 10 September and call again in order to cancel the number. I then asked them how do I then know I wont be billed for October again and it was said that I wont if I call before 12 September. How can I trust a service provider like that. As a customer I have been abused by you over the whole period of this disgusting relationship. I will be cancelling all of the contracts Im currently having with you asap because this was the very last straw..goodbye MTN...you lost a loyal customer of almost 20 years