Is there a zip oyster 16+ expert out there somewhere please? DD takes national rail trains to school each day. She always specified a monthly season ticket from home station to school station, not via London terminals. Since changing her 11-15 zip to the 16+zip this term her monthly bill has doubled in price from £24 to £46.70. TFL say its national rail's fault. National rail say its TFLs fault. Neither can really explain it or help find a cheaper option. I've trawled through all the terms and conditions but I am thick. Why is the bill double?