PostNet SA Waverley fails to deliver parcel

I went to the Waverley PostNet on Monday 01/02/2015 and requested my parcel to be delivered via courier the next day. I paid R185 which is the fee for Postnet2door. Today is Wednesday and I have a very frustrated customer who told me the parcel is still not delivered at close of business today. My customer is requesting a refund for the product mot delivered to the amount of R800. I was on the phone since 10H00 this morning and made several calls to Carin. She told me it is not PostNets problem but the courier company they use. How can I pay for a service and be told my parcel will be delivered the next day and it is not done up to know. Who is going to refund my customer who will give me a bad rating on bidorbuy?????