A relative has a chronic "for life" condition that will never improve. This is stated on all her medical records and documents including from very well known hospitals in London. There was a similar point where the PIP was going to be adjusted to the lower band? after a random, flawed, reassessment, but after pointing out that the condition hadn't changed, nor ever would (with medical documentation), they changed their decision... luckily in my relatives case it was never actually stopped.
Whilst I don't know any proper avenues for complaints as we didn't get that far, give them both barrels!