Eu estava com uma assinatura grátis de 7 dias no acrobat pro mas esqueci e aconteceu a cobrança de 20 e poucos euros, ainda estou no prazo de 14 dias de reembolso, como posso solicitar ele e onde?

you just need to cancel your subscriptions(s) during the refund period and refunds are automatic (taking up to 14 days to complete).

for info on how to cancel your subscription, this page describes the few steps involved, https://helpx.adobe.com/manage-account/using/cancel-subscription.html

make sure you check your account ( https://account.adobe.com ) after cancelling.  many people with an acrobat have two subscriptions: acrobat and ai for acrobat.  you need to cancel each, one at a time.