Air particulate filter fault code

Please can some one comment if this should have happened when I took a car in limp mode and fault code above on but driving? We asked for diagnostic test as fault code of the above and engine in low mode. BMW garage performed tests and then deleted codes to get out of low engine mode and proceeded air mass stress test at motorway revs and blew the turbo and ruined the engine. They are saying they are not liable. We will be $17,000.00 in debt with a car we can’t drive as needs. New engine. Everything I read in internet says you should fix dpf before proceeding with such test but they didn’t. They had the fire brigade called out. I really need help and I haven’t slept for 3 days.