times are hard for every industry - i should know i deal with warranty parts claims on a regular basis now - just like insurance companies they will do ANYTHING to get out of paying.
but to be brief
1, you car had a possible fault
2, you still remapped it
3, vw have done what any dealer / company will do these days - tell ya to go forth and multiply
I do feel for ya mate, but you havent got a leg to stand on - sorry - you modified the car from OE specifications - read the small print ( not that i think you need to )