Alguien sabe por qué no puedo agregar ningún método de pago?

you can try adobe support, but some countries are problematic. there are 2 ways to contact adobe support; chat and twitter (now x):

chat:
if you have or want to purchase a subscription, use a browser that allows popups and cookies
and click here, https://helpx.adobe.com/contact.html?rghtup=autoOpen
in the chat field (lower right), type AGENT
be patient, it can take quite a while to reach a human.

twitter/x:
tweet @AdobeCare

p.s. if you're contacted by anyone (via email or private message), it's much more likely to be a scammer than an adobe representative.