Registered letter of donation sent back to sender

We are an NPO and we received a donation voucher of R5000 that we had planned to sponsor our school kids with uniform on Madiba day from our centre. When the voucher came I requested the Kimberly branch to send the parcel to the post office close to my work as I could not collect from the post office I live by as their offices are already closed the time I knock off. I don't know what happened but the post office scanned the parcel back to the sender and the sender can not resend we have to reapply again during September month. I have made several calls to post office until I got hold of the Regional manager by the name of Andrew and he made it clear that there is nothing they can do as the mistake was already made and the parcel is back to the owner's possession. This is very sad as we have already collected the sizes and promised the families that we will be sponsoring them with brand new uniforms and those dreams of 44 families are now shuttered and I don't even know what to tell them that I am now not able to assist as promised. This is so unfair as the PO is not even taking accountability of their mistake... We will have black a Madiba day because of PO's negligence. ..