Why did my bill go up twice in the last few months?

In September, my bill jumped about $30 because a promo ended.  I chatted on here and found that I currently had the best deal and was ok with that.  Now it just went up another $15 last month.  I do understand that promos do not apply to taxes and fees and I see those went up a little for the annual price adjustment, but the amount under my Xfinity package also went up $8.50 and I thought that part was supposed to stay the same during a promo.