Maaco Franchise — body shop, vehicle/auto

I brought my car last November to this body shop. Paid $1, 200 cash to repair the rusty part on the rear panel of my car. They told me that they need to cut the rusty metal part and it will be replaced with bew metal plate. After 5 months and a half, the rust showed up again exactly in the same spot which suggested that they did not replaced the metal plate as per contract. I brought it back yesterday, June 21, my contact estimator have told me to bring it on Monday as return job. I called today, June 22 to find out if I can bring it back today, however. the estimator told me that the owner Billy Palumbo had said that the rust part guarantee was only for 90 days. My point is they never replaced the metal plate as per contract that I paid for. I will file a lawsuit against this MAACO in Linden, NJ