Dischem treats loyal customer terribly

I purchased medication at Dischem Woodmead on 10 November 2018. I was supp**** with half the quantity of one medication (15 tablets) while I was charged for 30 tablets. I returned to the store on 17 November to rectify it. The dispensary indicated that there is nothing they can do, except sell me more tablets. Given that I need this medication, I was basically held to ransom to pay for medication that I have already paid for, but not been dispensed.

In the interaction, dispensary staff were also condescending, saying things like "why didn't you come back within a day or two?" or "are you sure you haven't lost the medication yourself?". I find this extremely disappointing. Why am I, as a loyal customer for years, all but accused of dishonesty and expected to pay for a dispensing error?

The pharmacist informed me that they checked their controls, and stock, and are certain that they dispensed correctly. However, controls, operated by people, may fail due to human error or manipulation. All that was needed, was to acknowledge that errors may happen, and dispense the correct medication. Instead, I am now convinced that Dischem does not care about its customers, does not trust customers when they flag an error in good faith (expecting it to be remedied), and basically *****s from customers by making them pay twice for medication they need and cannot get elsewhere on short notice.