Am i an Account holders being taken for a ride here or what ?

On 2019-12-13 i bought an item to the value of R2399.20 and was charged on to my Woolworths account at Sandton branch. On 2019-12-20 I went to CR shop presented the original slip i got on the initial purchase to exchange the item for something else. As the sales assistant ran a refund into my account I was shocked to discover that the same item was refunded for R1799.00 the new prize not the original amount charged initially charged into my account. What happened to R600 difference no explanation. Wasn't i due for a refund equal to the original amount charged on 2019-12-13? Woolworths had i paid cash for the item how much refund was due to me? This is totally unacceptable!