Poor Services

I bought items on my Mr Price account, the account balance came to a certain amount and if you work out the monthly installment, you get a certain amount, when I looked at my statement, the installment was higher with a R120(current installment and amount due is not the same and this is a new account) , I emailed Mr Price and ask them to explain the reason for the above, I`ve asked for a explanation because I cant just pay for something i`m not aware off or for something I don`t understand, the consultants received my emails but they are not responding to me, can a Manager from the accounts department contact me in order to explain why i`m being overcharged, because I`m waiting for over 6 days for an explanation?