I have an account with Metro Fibre and my debit order is R400 every month

I have an account with Metro Fibre and my debit order is R400 every month. In December they overdebited me .R800 went off my account. I have logged queries and tried contacting them but to no avail. So disappointed on the way they are handling the issue. It's over a month without any resolution to the issue...I need my R400 refund back. They just debited me again. Very poor communication skills and ********.