debit order deducted at begining & middle of month

I've reviewed bank statements and have noticed that in addition to the debit order from my cheque account on the 1st of the month as a credit card installment, there is second deduction around mid month listed as a finance charge which is roughly about half the amount of my debit order. When my credit card was opened there was no discussion about this second charge and it doesn't make sense to me as it now appears that I am being charged double interest related costs.