My monthly bill was $105ish but all of a sudden it's $165 and I can't figure out how or why? I didn't sign anything regarding changes to my plan, it was just suddenly increased in September from August.
Compare your current bill with a couple of your past bills, and also remember to read the notes on each billing statement. That should tell you why your bill increased. It sounds to me, however, that your promotion may have expired and that you're now on every day pricing for your plan.