Tata Nano — TATA Nano automatic car within 3 years need to change the AMT unit due to oxidation since the car is used less often

I bought a TATA nano automatic twista brand new car from the company. I have been using it day today journey. Since the Covid affected and more of the journeys restricted and car did not use more often. This recent day I had to travel to city and I drove the car, my car suddenly stopped in the middle of the road. I called the company and they came and collected it. Couple of days later they informed me that AMT unit of the car need replacing as oxidation taken place and sensors are not working properly, also said its costing 800000 Sri Lankan rupees . which is half of the value of the car. Its unbearable fee and what guarantees the company can give that this same problem will not arise again.
It shows that AMT unit of the car is heart of the car. Company has used low quality materials which oxidation takes place easily. Sri Lanka is summer country how can this be take place.
I would appreciate if you can reply to this email as soon as possible
Thank you
Sujee