Ceed SW cylinder head torn, no warranty case

My baby has a cunning Zelynder head, in my opinion this is a guarantee case. Kia is of the opinion that it is not, since the last check-up date was covered for 2 months. If my damage would be connected with a delayed oil change, I would also accept this but which cylinder head is tearing from too old oil?! Also, where with a check-up no special inspection is done to recognize such a problem. Also my car did not show a motor problem. He ran hot once and then was quiet for quite a while until now, where he was constantly hot and went off to the factory town. Does someone with such a case experience and can help me? Thanks in advance