My problem: No admin, supervisor, or root credentials present on the sticker of the router at the back.
What I tried: I flashed a vanilla firmware directly from zyxel to get rid of the ISP restrictions. Doing that also deleted the username and password that Digimobil Spain ISP uses to configure the device: username: user password: user. So I’m locked out of the device everything else is fine. It’s working like a switch with wifi no possible way to configure or change stuff though. Also, U-boot is locked and needs a password generated from a seed. Using uart to interact with the device prompts you for a login that you don’t have. Also, the router generates passwords on first boot after hitting reset button or something to get rid of weak passowrds like: 123456 for the root to something generated based on the serial number of the router.
What I would need to fix this issue I’m having:
atse DX3301-T0
2400C00C09503316E000148493987B03118E
The atse command generates the seed we need to unlock u-boot and we need a calculator that generates a password from that seed:

Then we use this command to unlock uboot:
aten 1,363943360710703246723488897955
This is what the router does when it boots after reset or flashing of firmware:
Initial 4: beatmlink....
Initial 5: beptmlink....
Initial 6: besysinfo....
Initial 7: beaccount....
Changing password for root
Password for root changed by zytmproot
Changing password for supervisor
Password for supervisor changed by zytmproot
Changing password for admin
Bad password: too weak
Password for admin changed by zytmproot
zyGetAccountUidInfoFromFile: cannot find uid 'x:0:0' in '/etc/passwd'!file size of source = 182