waiting for difference on the amount refunded after settling my loan

I must say that i am not happy with the service I am currently getting from African bank to think that they were for me the most efficient when it comes to customer service. I paid off my loan a month ago after having called to get a settlement balance. my debit order went off for the installment instead of balance when i was refunded i was short paid. not am battling to get the difference, bearing in mind that as banks charge interest everyday when you owe them. I won't be paid interest from the date i have been waiting to get the rest of my refund back. not treated fairly as loyal customer.