Best answer by Ranjan Koodo
Pro-ration is the exact reason, Joan.You're always charged a month in advance. Since you added the data on Nov. 11 and your billing cycle ends on the 24th of each month, you were charged a partial amount of $4.67 for those days. You were then charged upfront for the upcoming month (Nov. 25 - Dec. 24) on your current bill, for $10.
Also, our current promotional plans might be more attractive and worth switching if you think they meet your needs. We currently have a plan available for $50/month that gives you 50 daytime mins, unlimited evenings and weekends + unlimited messaging (same as your current plan), but 2GB of data (twice as much as what you currently have). Plus it's $5 cheaper than what you're paying each month. Take a look here, but keep in mind that today's the last day of the promotion. If you're interested in switching, you can easily do so your self through self serve.