They treated me bad, gave me bad attitude when I complain to them, in fact they did not care whether I have a problem with them or not

They treated me bad, gave me bad attitude when I complain to them, in fact they did not care whether I have a problem with them or not. They say I owe them R10154.71, of which I was paying R465 monthly, so I was shocked to see the amount I owe them, I didn't use their data, of which I believe I don't owe them anything.