**** debit order

I complained about the **** debit orders for R99.99 going off my account in February and they were eventually reversed in February. However going through my statements I realised that one of the debit orders that went through in December was not reversed. The form I received from the contact centre which I have submitted says it will take 30 days to resolve the matter. Why is it taking so long to reverse a debit order which was clearly stopped previously and what is there to investigate if two previous debit orders were stopped from the same company that deducted the money in December?