FNB does not honor payment arrangements

If I could give minus stars, I would. FNB is unbelievable. I made payment arrangement for my account that is in arrears. When the end of the month came they took off 2 months worth of payments. When I asked for a refund, the advisor told me a refund isn't due because my account is in arrears. How can they just deduct money off my account like that. I made arrangements to pay my arrears, it's not like I just left it. I am shocked. I don't know what to do. I am so angry.