Try canceling mobile contact

I have sent in cancellation form and went to Telkom store in SA to cancel two of my contracts after they expired before I left SA but still I received invoice and demand payment. I also gave my wife a letter of permission to act on my behalf while she stayed behind in SA but at no time anyone at telkom wanted to assist her and only informed her that I must do it my self. I am working in New Zealand and the time difference make it impossible for me to call. Telkom is stil deducting money from my bank account although the contracts has expired and not active for more than 5 months. How do one get it across to Telkom that I do not want or use your services anymore