Personally I would contact my insurance company, tell them over the phone that you have already given them the details when you first made the claim. They don't require anymore information apart from the car registration and driver name and address, especially if the driver of the taxi is/was insured with the same company. If you don't mind me asking what company are you insured with? I've had a few run-ins with a few insurance companies in the past. In the end Katy you are paying them for a service, it is their job to retrieve the excess and I would advise you to put pressure on them.
Dizmo,