Ford ******** their way out of a warranty

A week ago my turbo blew. Under warranty I took it to Ford secunda. Technician said nut on the propeller came loose but they not going to replace the turbo because there is a after market exhaust fitted. I am a technician myself and I work on turbo diesel engines myself. Thats part failure caue my vehicle has full service history and only 66000km on the clock. Ive asked numerous times for evidence of aftermarket exhaust cause I wasnt aware of it. Ive also asked what could a exhaust do so that the turbo nut come loose. Still no answer or feedback. And to top it up even the foreman personally told me infront of a witness that these 2.2 ford ranger turbos dont last. Im furious because Ford is baking out of a warranty that they should pay because they KNOW its their product that failed