Unauthorised debit order

On Air is the worst company to deal with , I have a 24 month contract with them for R159 for a DSTV Explora , which I entered into in Sept/ Oct . Instead their are now taking three debit orders , of which two are unauthorised. And one of these amounts keeps increasing. the debit orders are as follows R 159 , R 169 , and R 338 I keep reversing and they just keeping debiting. I send them email about settlement no responde until today Multi-Choice please assist because this company is selling your product and then they take advantage by processing ******** debit orders once you agree to the DSTV Explora. This definitely unfair because this is my hard earned money am self-employed i really cant afford this havoc.