It is possible that the garage has advised you need a replacement Mechatronic unit which electronically controls the hydraulics required to change gears. This is a common issue on DSG gearboxes. You can make a complaint to your dealer and/or Volkswagen UK but there is no guarantee of a positive resolution given the age of the vehicle, even though the mileage is relatively low. A complete Volkswagen service history is essential for any chance of success. We would suggest having the vehicle inspected by an independent DSG specialist, as they may be able to repair the Mechatronic unit or replace it on an exchange basis which would potentially be considerably cheaper than a brand new unit.