Incorrect debit of my account

I pre-ordered fibre in July. Fibre is still not available in my area, and won't be for some time. So I cancelled the order and am in the process of returning the modem. Before I knew it, Afrihost took R920 from my bank account. They say they'll refund this when they get the modem, but this is NOT RIGHT! I did not give them permission to take money from my account whenever they feel like it.