You need to contact with them. If you continue to use their service, 2 weeks is okay(my experience), but it is better to give them one month. Ask them give you some promo. What I got is 2-years contract, around 25.xx per month. However I need to pay in full in advanced ($604?), which does not bother me too much since I will stay here for a while...
If you do not call them, yes, they will renew your contract automatically.