Incompetence is getting the better of me.............

On day 2 of the month I am told that my internet package has been depleted. How is that possible? agent suggested that somebody is hacking my account, using my password. I cannot even access the account myself, without consulting the very long and intricate password found at the back of my wifi telkom phone (landline) Last month the data was depleted after a week. I need to cancel my account. What would be the easiest route?? Anybody that can help? I cannot tolerate the incompetence of this company any longer. It will be a sad to let my landline go, but I have no choice......................