Paying more than i signed up for

I signed up for the 250package in june everything was ok.july my bill was 500 paid no stress, august my bill is 500 again.called the customer care only to find out on the 250 package there are setting i had to manage which i had no idea of,that lead to me paying 500 instead of 250. Like really for me to choose rain the idea was to safe not waste money on data. Am so disappointed