R50 less on CREDIT NOTE. Why?

2 Items were purchased on the 24 December 2015 and the price paid was R289.98. Details of the Invoice:<br> Store Code: 6766, Date: 24/12/2015, Tran No: 129675, Term No: 11.<br> <br> The Items were returned on the 26 December 2015 and the Refund Credit was R239.98, R50 less.<br> <br> Invoice details S/N: ***285, ***0 15:39:38, cashier Nomvuyiso Phakuphi ***.<br> <br> Please explain why the refund was R50 less. The items were purchased with a Debit Card and the money was returned in Cash.<br> <br> I first called *** and was given the Number ***. The mail box is full and cannot accept messages.<br> <br> The original slip was handed in at the store, Jet, Canal Walk.<br> <br> Please give me a Logical explanation