Typically when you change your ADSL modem from router to bridge mode you need to also change the corresponding pfSense interface from DHCP and enable pppoe on it: Interfaces -> (assign), click on PPP tab, add a PPP interface, go back to Interfaces -> (assign), add the ppp interface, assign it to WAN (or whatever) then add the username and password that had previously been configured in the ADSL modem for ppp.
I don't know if that applies to your service.