Yes, that is disappointing. It is most probably the carrier. I ordered a preprint
of my autobiography for a reviewer and tracked the delivery to the USA where
it stayed and stayed with the US PO service. I gave up on it ever getting there
and yet it did - weeks later. Generally it works pretty well.
There is a delay with print-on-demand and it may be that your book got caught up
with the Xmas traffic. But this is generally a few days at most. Expect to see your
copy unexpectedly. I see you are given a choice of 4 delivery options; did you go for
tracked?
I looked at the Trust Pilot reviews and there were only 7 reviews; 2 5* and 5 1*. But two of
the 1* reviews were complaints about the book quality which is not a GBB responsibility
but that of the author. Still its not much fun when your book disappears like that.
Mark