Changing my banking details with no permission

So this is how it goes, in june cell c calls me as im due an upgrade i finalizes the upgrade and i get the phone great service until the month comes to an end and my debt does not go off so i dnt pay attention as i dnt look at my debts and so in july i start calling customer service for random info and i cant pass security and i cant be told why which i get must its 3 of my personnel details i dno how i can get it wrong. I actually realised im calling to add a whatsapp bundle.

So i keep calling entre a self serve pin am told i cant be helped coz i failed security fine had to escalate to a manager who then comes and says did i ask to have my bank details changed after i told him i have never had my details changed since ive been with cellc besides the account details, fine that was useless and i was just getting more angry, but never was i told the payment never went off.

Month end is her its July and i never updated my details as cellc is now saying i need to pay for this charge of the payment not gng off in June.

Firstly who said change my banking details, and secondly i wasnt even sent any form of notification that it was changed nothing and now they cut my lines coz i still owe the bounced payment which im not willing to pay at all as cell c messed my account details, my credit scores and put my name in red as i cant even apply for a home. I am so ****ed coz i was also paying for a tariff i wasnt even getting and a late payment charge from january *** that made no sense at all yet im expected to do the runs and call i work i cant sit on the call all day as im placed on long holds and no solutions that i just end the call by saying okay

There is so much i wanna add but im so tired cell c is not the network you wanna join if thats what ur thinking i surely will cancel after my contract ends.