Sorry - must have missed the link of first read!
So I would make the initial appeal to GroupNexus / CP Plus Ltd on the basis of what you have said, namely; that the other documents were not served with the NtH.
In my opinion the NtH has a number of other failing;
1. The NtH fails to reference the original NtK as required by 14(5)(b)
2. The NtH fails to identify the creditor as required by 14(5)(e) - CP Plus and GroupNexus are now separate legal entities with different company numbers etc so it is unclear who the creditor is.