HI,
It’s clear that the router can communicate with the ISP’s PPPoE Acces Concetrators and those reply with the message “failed to authenticate ourselves to peer” because either the credentials are wrong, or not implemented correctly by the ISP, or, there is an encryption mismatch between client and server.
You could try to check under PPP → Profiles, click the default one, and make sure that under Protocols tab the “Use Encryption” setting is set to “Yes”.