You can't do anything unless you can get the CEO and former employer to agree to not enforce the contract, in whole or in part--that is, if the contract is a legitimate one (e.g. not for anything illegal; no fraud was committed in getting you to sign it; etc.). That's because a legitimate contract which someone voluntarily entered into is enforceable against him or her, regardless of the motivation of the other party. You may wish to bring the contract to an employment law attorney, and discuss the situation of how you signed it in detail with him, to see if there are any grounds to invalidate the contract.