A letter to the Traffic Commissioner detailing the company's apparent indifference is always worth a shot. Address for the Western area Commissioner that covers Oxfordshire is 2 Rivergate, Temple Quay, Bristol, BS1 6EH. Telephone: 0300 123 9000. They tend to get filed with the vehicle operators's licence details.
The thickness and contents of the file is taken into account when deciding if an operator is of good repute and is managing there business in a responsible manner next time the operator's licence comes up for renewal. One complaint and nothing is likely to happen. However a series of complaints (not necessarily related) can result in an interview which will make the grilling the chairman of BP is about to receive from a congressional hearing seem like a walk in the park...