Edgars Charges Interest Illigally.

I have just received an account statement from Edgars that indicates that they are transgression the National Credit Act. I have a 6 months zero interest account. And I bought clothing from Edgars with the cost priced in. I have now received an account that stipulates I must pay 17.5% interest. This is ******* as I have not been assessed to confirm I can pay the account, I have also not been informed of my rights, I have also not been informed of the interest to be charged for purchases as I clearly had a 6 month zero interest account and finally the total cost of buying the items of clothing, including the interest cost has not been explained to me.