Change from QR to Thru-Axle not working

Hi,

after one season I need to switch bikes from Quick-Release to Thru-Axle. Therfore I first removed the DS-QR-adapter -> easy

Next I tried to unscrew the NDS-QR-adapter with a 5mm-Hex-key as well, but the adpater would not move at all to the point that the hex-key wasn't getting any restance any more...

Then my only option was to use pliers on the 'outside' of the NDS-QR-adapter which was very hard and painful but finally I was able to 'unscrew' it. This is what both adapters look after unscrewing:

The theads on the NDS-QR-adapter obviously are completely wasted...

Next I tried to screw in the NDS-12mm-adapter which was only possible with a quite some force and possible for only two or three turns... I then unscrewed the adapter and this is what this adapter now looks like:

 

Not only are the threads on this one destroyed now as well but also the inner diameter seems to have 'shrunk' as it is not possible to get a 12mm-axle thorugh it anymore...!!!

So what is going on?

Why is this Neo 2T 'destroying' all of the NDS-adapters (which all seem to made of rather cheap and soft aluminium)?

And how shall I proceed from here on now?