Poor Customer Service

Bidvest spent more R20 000 to take down the engine for my car at Autohaus centurion but just after collecting the car, it had oil spillage & oil pressure warning light. I sent my car back to be repaired again, VW Autohaus wants to charge more, is that fair? not at all because the above oil issue forms part of the engine that was taken down. what is the guarantee on their job? car is currently sitting with them & they are not saying anything