No one can answer your question without reading the contract. If, in fact, your employer has breached a material term of the contract, you have certain remedies available to you, which may include being relieved of any further obligations you have under the contract. But this is something you must review with an attorney, as well as discuss the details, in order to get an informed legal opinion and be apprised of your legal options.
They say you get what you pay for, and this response is free, so take it for what it is worth. This is my opinion based on very limited information. My opinion should not be taken as legal advice. For true advice, we would require a confidential consultation where I would ask you questions and get your complete story. This is a public forum, so remember, nothing here is confidential. Nor am I your attorney. I do not know who you are and you have not hired me to provide any legal service. To do so would require us to meet and sign written retainer agreement. My responses are intended for general information only.
It could be a valid reason for terminating your contract. But you need to have an attorney look at the contract first to be sure. Go see an employment attorney in your area before taking any action.
I agree with the other attorneys' answers. The words in the contract are key. If the company "materially" breached the terms, then you may be ok. If it was a mistake, then maybe not. It is probably worth it for you to have an attorney analyze your situation after reading the contract and speaking to you. You can probably find an attorney to do this via phone/email at a low fee. 949-481-6909.