I've used this: https://usuariosteleco.digital.gob.es/reclamaciones/telefoni...

Used my digital certificate (which is installed in the browser), but AFAIK, you can use Cl@ve on that page above too.

In the past, I've cited BOE-A-2022-10757 (https://www.boe.es/buscar/act.php?id=BOE-A-2022-10757), done a reclamació for the repeated loss of lawful access on my connection, and a denúncia about a broader overblocking practice affecting access to lawful services.

Also, supposedly, we should be able to make claims to CNMC as well, but haven't figured out how. Also of course, been complaining to my ISP every time it happens too.

I think this is it: https://reg.redsara.es/#login