Dexter Axle Company changed their "axle warranty" in 2016 from a 2 year warranty to a 5 year warranty on sprung axles and a 10 year warranty on Torq-Flex axles.
So, your axles are warrantied by Dexter for 5 years. Keystone never warrantied your axles, they "managed the Dexter claim" for the first year, then it's up to the dealer or you to contact Dexter with problems. Your dealer is not doing his job if there's an axle problem and he told you it's not under warranty.
If you don't have a copy of the Dexter warranty, you can read about it and download a copy here:
https://winstontrailers.com/whats-ne...axle-warranty/