New Customer Internet Service Promo price not honored?

Hello, I am a new customer as of last December and I switched from another internet provider due to Cox offering a $30 monthly price for internet with no overage costs. Now I am seeing on my bill that Internet price has already changed to over $50 per month. Why can't companies seem to honor their agreements? I thought I was locked in for 1 year at the $30 per month price. Now I am going to have to look for another internet provider again. Disappointed.