3 weeks and no refund for online purchase

I did an online purchase for River sand and cement which I needed ASAP as I was busy with a home renovation. However the transaction showed unsuccessful on the website, but payment went through on my fnb account. Builders requested for a pop to verify, so I emailed to them, I requested for them to send the material as it was urgent, however they declined my request. It then took 1 week for them to allocate the funds to my builders account,i then requested for payment to be refunded to my bank account, I filled out all the necessary paper work and emailed to them. It's now been another week and half gone by and yet no refund. I can't understand how *********** such a big chain store can be and to make me go through all the hastle, when the problem of the transaction was on their side. I will not be buying from them again and will rather purchase from another hardware store.