service is worthless for the Gym

I have joined planet fitness for a 12 month contract, and I did pay upfront membership fee fro 12 months. now I want to cancel the membership as I couldn't attend to the Gym, and they are charging for cancelation fee of 779 and they also have some sort of stupid rules saying that if I don't attend for 12 times in three months they are going to charge me extra, as it depends on my concern whether I can attend the Gym or not how can they charge me for that, really useless service and I suggest people not join planet fitness if they cannot attend on their own regular basis, and now I have a four months contract period left and they say I still owe them for cancellation. ****ing useless service by planet fitness.