Tilting lever bar broken after timing belt change noticed

Hello, my Renault Trafic was built in 2004 at 200,000 km after the rotational timing belt change, the tilting lever bar was broken during the drilling of the 3rd cylinder. The timing belt change was carried out by a free workshop. The workshop informed me after the change that the engine was running unevenly and that they were still on the troubleshooting. The timing belt was removed several times again and put on, only with universal tool, then with special tool, no error. Later it was found that the tilting lever rod is broken and the engine is not running round. compression has been measured and is fully there. The workshop makes a competent impression on me. Nevertheless, the vehicle has worked perfectly at the time of delivery and the workshop thinks that this must be a pre-damage. What do you say about it? First of all, thank you for your feedback! Best regards!