Welcome! My goal is to do my very best to understand your situation and to provide a full and complete answer for you.
Good afternoon. You can rescind the sale. A seller is obligated to disclose anything the seller knows or should have known that a reasonable buyer would consider material in making the decision whether or not to buy the car. Advertising the car as "certified" when it is not "certified" qualifies as something that a reasonable buyer would consider significant. Thus, you have recourse. If the seller is not willing to remedy the situation by refunding your money in full, raise the stakes on your seller by letting the seller know you will be filing a claim not only as a breach of contract
case, but also as a deceptive trade practice
action, which will entitle you not only to actual damages, but also an additional amount equal to multiple times your actual damages as punitive damages. That typically provides plenty of incentive for the seller to settle this on your demands rather than to face the possibility of these punitive damages; but, if it does not, file the suit.
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