Why am I paying for something I do not receive?

As convenient as on line shopping can be especially for mall dislikers like myself, however I am disappointed in their “next day delivery”. On two occasions I have paid a fee of R39 to have my order “at my door step before 17:00 the next day” and on none of those times has that happened. I paid for a service that I am entitled to. It’s easy to let go the first time, however clearly this is a service they cannot keep up to and it is disappointing considering that there is a fee to it. No email of apology is sent if there are matters beyond them that are excusable to them not delivering as promised.