Netflix has actually raised prices multiple times, but it's also possible that you got automatically upgraded to a higher subscription tier - happens pretty often when contracts expire or something changes in your account settings. Check your account settings to see what plan tier you're on right now and compare it to the one you signed up for back then. If you're on a more expensive plan by accident, you can usually switch back without any problem, but sometimes you have to deal with fewer simultaneous streams or lower resolution - is that okay for you or do you usually watch on multiple devices at the same time?