It's only sneaky if they didn't explain up front that the promotion was only for a 12 month duration. If they did, then you got something cheaper as a promotion for being a new customer thus benefited. They could have charged you full price if you would have preferred?
People need to take responsibility for noting when deals and promotions come to an end and then proactively decide how to continue, if at all. In this day and age everyone wants spoon feeding and/or expects loyalty from companies - but it's too late, the American influence of capitalism at all costs has taken over.
Show no loyalty to companies (unless they show ethical behaviour, and / or provide you a service that exceeds expectations / quality). Companies will show you no loyalty, so your only option is to be a savvy purchaser and follow what's best for you and your requirements.
Our British cultural norms of being loyal has been taken advantage of by business in the main so you now need to play the game if you want to gain out of the market we are in. Do your research, search for best deals, threaten to leave, and ensure you do leave if they don't give you what you consider fair. It's a race to bottom, so make sure you are not squashed