Nedbank deducted my home loan twice this month 12 and 13 if December

Nedbank deducted my home loan twice this month 12 and 13 if December., causing unnecessary bank charges. My debit order is suppose to be on the last of the month as per bank mandate I have signed .Last month Nedbank failed to debit at all , I had to call by myself .I request immediate refund on incurred bank charges .I am very disappointed with Nedbank system errors and ka k reliability.