Message: "Reduced engine power"

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Two months ago the following warning messages "Reduced engine power" and "Visit service soon" started to appear on the instrument panels display. At this point, the actual engine power was also reduced. After the car is stopped the ignition turned Off and On again the messages turn Off and the engine power is restored. Unfortunately, every time the car accelerates or the cars speed exceeds 80 km/h the messages reappear and the engine power is reduced together with the illumination of the MIL warning light.
DTC P0101 was the only fault code retrieved by the scan tool.
The car was taken to a workshop where they diagnosed that the DPF filter is oversaturated. Unfortunately, the workshop that specializes in DPF cleaning services just cleaned the filter and installed it back without inspecting the filter. This job included the resetting of the DPF filter values in the ECU. The invoice included a remark saying that the "Turbocharger needs replacement - oil in DPF filter".
After verifying with the workshop that it is safe to drive the car and that I should arrange to have the turbocharger replaced in another workshop. After driving the car for around 15 km in city conditions and after exceeding 80km/h the same messages appeared again, the car entered into Limp-home conditions, the DPF warning light illuminated and the car emitted heavy black smoke from the exhaust. I drove the car another 5 km to my house in the Limp-home state and contacted the DPF workshop and told them what happened and asked what to do. Their reply was - We warned you about the turbocharger and you drove off so you're responsible for the damage. No warranty.
OK, I arranged to have the turbocharger replaced in another workshop where they inspected the DPF filter and found out that the filter is completely burned out after driving some 50km! Apparently, the DPF workshop used an exhaust sealing paste that damaged the DPF filter!
My next steps were to source a new or good used OEM filter. I don't trust the aftermarket parts.
New OEM DPF filters are available with a price between 3 300 to 5 000 Eur. In the end I discovered a used filter in Belgium with low mileage that was visually OK and was only 480 Eur.
I had the car towed yet to another workshop to have this DPF filter installed and cleaned. This time the filter was cleaned using a dry method. After cleaning and filter installation, I collected the car and after driving it for about 5 km the same messages appeared again together with reduced engine power and black smoke from the exhaust during acceleration.
I called 8 workshops that repair Chevrolet and was refused by all of them for the following common reasons:
a) I am not going to repair car that has been worked on by so many people before me
b) I don't have the required Scan tool for this specific car

Can somebody please help and recommend what should I do now?

Thank you