WHY DOESNT THE LID OF THE NEW TOILET DOESN'T STAY FLUSH TO THE SEAT

We had new bathroom sanitary ware fitted when we had renovation, we moved back into the property last month and its been like hell. Too many things wrong, and even personal items damaged. We had enough of the builders, who took our money and left incomplete jobs and left us in lots of financial difficulty, we dont ever want to use those builders again. One thing We would like to know is why the lid of the new toilet doesn't sit properly on top of the toilet seat? Does the toilet seat belong to a different toilet? I'm very suspicious as it even looks like it a second hand one when it should have been a brand new one., also it has lots of scratches on it. I asked the plumber who fitted it but he wasn't helpful at all.