How can I terminate my employers contract!

I am currently working at a school in jeddah as an expat teacher. They advertised the job role as 12 months and my offer letter states that my salary will be paid in twelve months. Once I was signed the contract I realised that it was a 2 year contract instead.
Secondly, on my contract it states that I get 30 days paid leave during the summer but apparently we only get half our salary. Thirdly, they expect me to act on a role of lead teacher without any further explanation and idea of duties.
I am not happy with the contract. I realise I should have read it thoroughly before I signed but they mislead me tk believe it was 12 months.