How does Clicks problem become the clients problem

I received a call from Clicks Zevenwacht pharmacy about 3 week ago saying that my payment of medication does not reflect on the system and if i still have the receipt. I then said i would have a look if i have it. I then returned the pharmacist call to let her know i dont have the receipt i then told her what i paid at the front desk where she told me she is going to check if there isn't another profile. I returned to clicks Zevenwacht today and was told they cant process anyting due to non payment. I how ever want to know how this became my problem, medication go's out in sealed steel boxes so what happend to the payment i made and how is this my problem i was so mad today.