In this unusual case, we would recommend trying the following:
Put the cage into the vehicle, while the cage is flat, then assemble the cage inside the boot space. This works as the boot entrance can be narrower than the space available.
Do your rear seats move forward, like how to the front seats do? Then move them forward a notch or two, this will solve most cage fitting issues.
If these do not help you get the cage to fit, then send us an email and we can look into what options are available. Send the email to firstname.lastname@example.org