but I'm not sure what you think you should get to be honest.
I use the guaranteed delivery service (sometimes called special delivery) all the time to send stuff to clients, and it works almost every time. On the rare occasion there's a glitch - and it is rare - I get the cost of the postage refunded, which is fair treatment in my book.
We seem to be degenerating into becoming a compensation culture, whereby everyone expects some form of recompense for every little thing that goes wrong in their lives. I know that we should strive for perfection in all things, but big postal delivery services are run by human beings, they depend heavily on transport systems run by other human beings, and sometimes people make mistakes - we all do it.