B probably exists so they can split fiber between multiple end users or support things like phone service over the same link. Did you use the same VPI and VCI?

B probably exists so they can split fiber between multiple end users or support things like phone service over the same link. Did you use the same VPI and VCI? PPPoE also sends an identifier (the "Host-Uniq" tag if I'm understanding it right) that probably has to match what your ISP is expecting or has assigned.