Mahindra Avoiding Responsibility

I bought a Mahindra Scorpio from Mahindra Durban in 2018. An extra fitted to the vehicle was a bull bar which within a year had started rusting badly. Mahindra Durban closed down and I subsequently dealt with the garage in Pinetown. I showed them the rust but after much debate lasting over a year they conclude the bull bar was not there responsibility, this despite the bull bar being purchased under a Mahindra invoice and there being unable to give me a name of an alternative supplier.