From R399 to R600 a month

Cant belive this is what i signed up for!! i singed up for a R399 capped contract and now when i get my bills its sometimes R600, i asked to be deibted but still nothing i have to call in everymonth and make manual payments when telkom decides to send me the invoice.First month i paid R889 went off my account, Then manual payment of R590. Now that is still outstanding. Im in the process of buying a car and this is affecting me. please sort this out this morning.