Incorrect billing

I app**** for an Apple Ipad Mini at FNB online banking. There were a couple of different options available but I took the one for R199 per month for 24 months without a simcard because I had my own. I even discussed the matter with two of my work colleagues and they also said that is the better and cheaper option to take. I ordered the Ipad Mini, for the R199 offer and my offer was confirmed with a printout I made. I waited a few weeks for the Ipad because they didn't have stock when I phoned and followed up. When the first debit order gone through on the account it was R265 and I thought maybe it is additional charges. From there I pay R265 every month!!! I queried the matter with FNB but they just say I took the R265 option which is not true. Unfortunately I threw away the document with the proof of the R199 option. But as a FNB banker I trusted by BANK!!! And now this. Why would I take the more expensive option if I have a cheaper option available. I don't know how to solve this matter because I threw away the proof but if the proof was sent to me they surely should have it on their system. I am really disappointed! Regards Janine