Update:

Voltz just contacted me with this email:

Hello!

I saw your post on Stacker News through Calle's notice, who helped me understand how to recover your funds from an old keyset.

What happened is that there was no censorship; the issue was due to the incompatibility of a deactivated keyset. This is very different from censorship—it was disabled for security reasons. But anyway...

After running a separate mint in a controlled environment, we managed to retrieve the proofs of your eCash and recover them. So, I’m sending you a token of 20,015 sats from the recovery, which you can withdraw at any time.

We apologize for any inconvenience caused so far. See you!

-------cashu token string-------

With this I was able to recover the funds.

Big thanks again to this forum and to @calle for supporting in the recovery. I decided to donate the recovered funds to @calle.

To summarise the situation with Voltz:

• I would have appreciated if they had disclosed somewhere publicly, or at least on their website, that they disabled the keyset. If I had known what was going on, I would not have reset my wallet and the recovery would have been much easier.
• I would also have appreciated if they had taken some initiative themselves in contacting the Cashu team in what can be done about this issue, instead of just deciding to ignore me until I created this forum post.