UNPAID BLANKET BOX- REFUND

Bought a KENTON blanket box online, did not get it when I went to collect physically in store. they said the amount I HAVE PAID( which is the R799, that was written on the advert) IS STILL SHORT as the item is R1 099.

They then offered to refund me and requested the proof of payment. There is no type of proof I HAVE NOT SENT BUT THEY KEEP SENDING ME FROM PILLAR TO POST. IT HAS BEEN MORE THAN A MONTH NOW DRAGGING, TELLING ME THIS AND TELLING ME THAT...