Double Debit, Refund Declined!!

I have been a loyal client. and have been paying for my loan installment on time for years. I missed a month(s) of payment, because my account was not debited. I was sent an sms that arrangement had been made to help clear the arrears, I missed that sms, and requested a refund after the debit order went off for the arrangement without my approval. After calling African bank, we made arrangement to clear the arrears, for installments much less than what African bank initially debited my account with, and one that I could afford, but they still declined my refund request. This has severely impacted my budget. This bank is very inconsiderate!!!