Wrong amount debited on my account

The beginning of September i had sent out a written and signed letter to reduce my debit order amount to R500 as i had lost my job and would increase it back to R1000 when i get a job again but at the end of September i got debited R1000 which i did not budget for. i asked for a callback from on your website but to date i have not been called regarding this matter.

Kindly advise?