Rain Account increasing month-month

I noticed my account with Rain went up in the past 2 months. From R739 in July to R757 in August to R 834 in September. I have logged multiple support ticket to try and get answers why my account is increasing month to month but no response. I was reminded by Rain every time and again to please activate and use the sim cards delivered to me. Eventually I asked my son to please start using a sim card as it free. I thought the increase on my account might be because of the additional sim we using but upon investigation I saw that it states on every webpage the sim with data, minutes and sms's are free. I cant understand why my account is increasing. I just need a Rain consultant to explain this to me. Before I know it my account will be over a R 1000.00 per month