Refuse to refund my R100 airtime unfit for use

The Howard Centre branch of Pick 'n Pay has just refused to refund the R100 Telkom airtime voucher I recently purchased that was unfit for use. I bought the airtime last week to top up my Telkom LTE router, but the voucher would not work. When I called the Telkom customer care line they said the airtime was unfit for use due to the fact that I have a Telkom contract. The Telkom salesperson on the line assured me that Pic n Pay would refund me for the airtime that could not be used as she topped up my data by adding another R99 to my debit order. Today I went back to the Howard Centre Pic n Pay and was told flat out that they would not refund me. I asked why their refund policy was not on display to customers and the manager told me that it was (pointing to a sign) as I walked over it was clear there was no refund policy to be seen and surely a MANAGER would be aware of this. In addition to this cashiers do not advise customers that airtime is not refundable. Upon looking at Pic n Pay's refund policy online (please see below) there is nothing that states that airtime is not refundable. According to Pic n Pay's own refund policy, goods will be refunded if 'unfit for use'. REFUND!!!!!