Debit Order Dispute

A debit order was loaded onto my account not for the first but second time without my approval. I noticed the debit order on on enquiry to have this reversed have been referred to the provider whom I have no idea who this could be. FNB are allowing individuals/companies access to my account without my consent and now make this my issue to resolve. I am not happy and have asked for my account to be closed but they are just ignoring me. Can someone please assist with having this resolved.