Rain Theft

My son asked me to buy 2 Rain simcards as it does not require a contract to have these sim cards. i logged onto the website to purchase there simcards. a month later R10045.09 was taken from my bank account. the more I quiried this the more they stated that i agreed to the payment taken from my account. This was a once off payment of R100 for purchase, note purchase, not à contact, a purchase of simcards for a R100. Can some one please assist as to how I can go about getting my money back from Rain .. I was Retrenchment and that was my monthly salary contribution...