That you chose an irreversible payment method doesn’t exempt you from any regulations about customer service.

Which ones exactly? I.e. in Germany, while you need to provide a phone number, you are in no way obligated to offer any customer service. Actually most sites don't have customer service but instead redirect you to FAQ articles and AI chatbots. People can send you letters via snail mail, which might have some legal merrit. Different regulations for some services, such as banks etc. But phone or email support is in no way mandatory if you run a website and charge 5cent to read an article.