So disappointed with Mahindra!

We bought a new Mahindra in November 2018 , the car to date has done 9352 km. About 2 weeks ago it rained heavily and the front window leaked water so badly that it ran onto our fuse box and our brand new immobilizer under the dashboard. The fuse box was damaged and the immobilizer that we had installed for R2500 completely destroyed. We took the car to the Mahindra agents and after verifying that the window had been badly installed they replaced the fuse box and fixed the window but refused to pay for the immobilizer. After I repeatedly phoned and I also wrote them a letter they agreed to pay for half the cost of the immobilizer, take it or leave it. I feel that they should replace the immobilizer in full as Mahindra is in the wrong due to the bad assembly of the window. Now we are having to use the van for the business and if it should be ****** we will not be covered by our insurance. Please inform me as of what course I should take. Many thanks PAOLA GIBSON for Intle Design