new Chevrolet engine seized

We bought our bakkie Chev Utility brand new 6 August 2012 Took the bakkie for regular services to GM Louis Trichardt. Until we took a drive to Polokwane on the 28th August 2016 while driving on the N1 the bakkie started to jerk we stopped at the nearest garage poured petrol just tried to start the bakkie again when we heard a loud bang noise phoned the tow truck service in Polokwane they towed the bakkie to Westvaal Polokwane. Westvaal Polokwane phoned us to say the engine has seized, we wanted to know the reason why, because the bakkie has been for regular services at GM Louis Trichardt, they first said it was the starter, then a few days later they said the alternator needs to be replaced and then it was the engine seized. We could not understand why, because the bakkie is still new and under warranty. We then found out GM Louis Trichardt did not sign the service book for the second and third services they have done. We went back to GM Louis Trichardt. They checked the first service which was signed by them but did not appear on their system just to find out the bakkie was serviced under a wrong registration number and the wrong VIN number. I think that is why they did not stamp the book the second and third service the fourth and fifth services were stamped. Onnette at GM Louise Trichardt said there is nothing they can do now. Chantell Du Plessis at West Vaal Polokwane said we have to pay for the new engine . They replaced the engine which cost us over R55 000,00 cash we arranged with Chantell to have our seized engine back. When we went to fetch the bakkie. Chantell was extremely rude. Firstly she did not greet us when we walked in when we asked about the engine she said I don’t have time to argue with you people I have work to do and she walked away next the manager Hennie came telling us the engine belongs to GM, we had to pay another R6500.00 if we want the engine back,. We paid for the engine, left when we drove for 50km we stopped at a garage just to find out the under carage protection cover was not replaced, we had to drive all the way back. In order for them to refit the coverplate. We are extremely unsatisfied with the service we received and would like GM South Africa to contact us URGENTLY with a solution