So a couple of months ago Netflix made the decision to separate it's DVD and Streaming plans for subscribers. It grandfathered all current subscribers for a couple of months, well the time is up and you'll need to choose a plan or pay up.
If you choose to do nothing by tomorrow, Netflix will assume you want both plans. That's logical but it may be something you didn't think about. After Thursday, each plan will cost $7.99 per month, or $15.98 per month for both.
To make a change, go to your Netflix account