Peugeot 3008 weld rusted on the pipe from the engine to the catalytic converter after 5yeras 3 monts and 39k on the clock

the weld has rusted and broken from the engine pipe to the cat, after 5 years3 months with 39 k on the clock, was this weld fit for purpose when the average life of a cat is 100,00 k or 10 years. should i go to court on this issue. i feel because the car was always serviced by Peugeot the rust would have started some years ago while the warranty was in place. they want to charge me TO REPLACE THE CAT
your opinion please
Thank you
Terry