Misleading

I rented a vox battery. They have 2 options 12 or 24 months. The 12 month is more expensive than the 24 months. After 10 months they've put up the price. I complained because I believed it was a 12 month contract with the price staying the same for 12 months and I believed after 12 months the hardware would be mine. Apparently I believed wrong. But its misleading advertising. How can you have a 12 and 24 month contract which after the 12 or 24 months continues and the equipment isn't yours? I'm pretty sure I could buy a similar battery on takealot for the same price.