Taking advantages of clients

Took my car for to the dealership in krugersdrop for not starting matter magnite still under warranty. And alexandra from nissan called to confirm my personal details and she confirmed it was under warranty.they worked on the car and called today to tell me i owe their machenic for adjustment of plugs the guy was rude and demanded i paid which i never gave any authorization for it at a fee. Now they refusing with the car due to the payment i dnt even knw and was never informed of. The car was from a service a mnth ago and they could have picked up the loose plug problem.im sure that's how they cover for their towing fee since they say its free. Im refusing to pay for something they didn't discus with me