Account was open on 12m without my consent

I opened an account on Saterday at Edgars Menlyn in Pretoria and collected my card yesterday. Today I purchased some clothes at the Woodlans Edgars Branch. I got to the till to pay on my account and when I asked for 6m they told me that my account was opened on 12m however the lady at Menlyn that assisted me when i opened an account NEVER asked me on how many months I wanted to pay back when I opened my account. So I went to customer serves and they assisted me and told me that the only way I can change it to 6m is to close my current account and open a new one. I am FERIOUS and a very UNHAPPY customer as I now need to pay rent on my purchased amount and that is NOT what i wanted!!!! It is unacceptable, the sales employees must explain to new customers and ask them what they want and not assume and proceed with out a customers consent.