Refund policy

On Tuesday 2020/09/01 at about 14:45 i was at Truworths cresta store and I bought few items there. On those items I bought a black coat that was selling for R749 and it was a small size, then on the following day Wednesday 2020/09/02 I went to the same store to exchange for size medium but the store manager told me that I have to top up with R150-00 because the went up with R150 . I felt very unfair for me to pay R150-00 extra for the same item that was still in good condition and it can still be sold again to the other customer with the same price. I was told that the only thing I can do is to refund and leave the coat at the store because I didn't have extra cash. Item code is ***1. I will appreciate if someone from Truworths can take my complain into consideration as I didn't get any help from the store manager even customer service