If the axles are being damaged that rapidly, I'd be questioning why they aren't replaced under warranty AND why you aren't being charged the proper TSB rate of $350.
This is NOT your problem to solve and there is NO EXCUSE for them trying to charge that much money for their bad design that clearly hasn't been fixed in your case! Maybe they aren't even installing it properly? They have MORE THAN ENOUGH telematics data available to know that you are or are not abusing your car in any way that could cause these to fail that often. They need to prove this is your fault, or start eating the costs until they figure out how to solve it.
Paying them is just rewarding them for the bad behavior.