New Honda Bike Rusts in 3 Months

Bought a brand new Honda Adventure Sport, their flagship adventure bike, in June 2019. After the 1000km I noticed severe corrosion and rust on the welding joints on the frame. Took the bike back to Honda 13 September. Finally after much pushing, I received a letter from HO, the “alleged “ corrosion is due to poor maintenance and I am responsible for repairs. How is it possible to rust a bike in 2 months? They seem to suggest I’ve used washing detergents of some kind that has rusted the bike. This is simply not true. This is my 11th bike, I only use water to spray down after an adventure ride. Bike is still at Honda( I refuse to ride it, internal rust is possible therefore dangerous).