Cashback was unfairly declined!
As stated in the terms and conditions on the Quidco website, cancelling, returning, or amending an order can result in your cashback being declined.
In this case part of the order was damaged on arrival. Next sent out a like for like replacement and picked up the damaged item. This was logged on their system as a returned order, therefore they were able to refuse the cashback.
Very unhappy with this as the cashback made the difference between Next and another furniture supplier. Won't be using them again.