You are going to have to do what you need to do on those upstream devices to make it work, it sounds like.
If they can do some sort of PPPoE pass through so pfSense itself is the PPPoE client you will probably be happier.
If not, the first thing I would check is that IPsec on both sides is set to use the public IP address as the identifier.
If you just set My IP Address as My Identifier on the left side and connect to 124.107.X.X, and they are configured to expect 180.190.y.y as the identifier, it won't work.
If you configure the left side to be My Identifier: IP Address: 180.190.y.y it might work.
If those PPPoE addresses are not static (you get the same assignment every time), but dynamic (they change), you will probably have to move to setting the IDs on both sides to a distinguished name set to a dynamic DNS name that change with the PPPoE address.
PPPoE pass through on the ISP devices is probably the easiest thing.