Truworths online complaint

Very disappointed with Truworths online. I bought a dress for a wedding the 9th of July at Truworths Tygervalley in Cape Town. It was a bit too small though, but I still bought it just in case I couldn't find a bigger size. The store convinced me to buy another dress from their online store and they assured me they do this often. So I ordered and paid for it, one size bigger. Their system couldn't show where exactly my size was, but it did show that in Gauteng there is at least 3 stores that has my size, so it will dispatch within 24 hours and reach me within 7 days. So this morning, 6 days later, I receive and sms that my online item is no longer available and they will refund me. Why?? Was it left till the last minute? Cause if it was actioned immediately there would still be stock as the system showed!