Need assistance for Pete 386 Cumminx ISX 13 speed motor

Hi my father has a Peterbilt 386 with cummings ISX 13 speed motor. He had some issues with the truck and had check engine light. Took the truck to peterbilt, they diagnosed faulty boost sensor and it was replaced. Then after 2 days check engine light came on again. Again took to the same place, they said this time the Turbo Speed Sensor has failed, they replaced the sensor and truck was road tested. After couple of weeks check engine light came and then changed into stop engine. Got towed to peterbilt, they hooked with PC and found severe EGR calibration failed. They cleaned DOC and DPF and replaced EGR valve. Again after some time the stop engine light came up and changed into Stop engine. Took the truck to Peterbilt, they said the old o-ring was left in the turbo speed sensor which caused all subsequent problems with EGR and turbo speed as well.
We went back to the original peterbilt location where initially they had worked on boost sensor and turbo speed sensor. They denied everything that cuz of their fault these problems raised. We planned to case a file against them. They have filed a defence for obvious reasons, they are denying that EGR was related to any problems in turbo.
I need your assistance if you could help me determine, if all these problems that arrived could have been caused through the initial carelessness when they worked on Turbo speed? Any to all assistance would be appreciated. If you are in Canada, close to Brampton, if I could see and and show you the work orders. My next hearing is on Jan 16. I spent around $10000 on everything, cuz of there negligence. please help. Thanks in advance.