PAYMENT REQUESTED FOR TRANSACTION NOT AUTHORISED

I lodged a complaint on 10/03/2015 regarding Nedbank allowing a ********** transaction of R1 085.68 to go through despite me having no sufficient funds on my account. I was told to FAX a dispute form which I have successfully done so on 11/03/2015. More than a month later, I still have not heard a single word from Nedbank even to acknowledge having received my Fax. Now I get calls requesting an increased instalment payment for a transaction that I don't even know & never authorized. I'm not paying a single cent more than my usual instalment because I knew how much available credit I had. Nedbank is allowing ****** to fiddle with our accounts by allowing payments that are way more than our available limit to go through. I need that transaction to be reversed.