Online Nightmare

Such poor service from Mr Price Home, I made an online purchase and at the time of the purchase there was a R400 off promo. I cancelled the furniture order which was never delivered to me which had a delivery cost of R400. I had to follow up multiple times about the refund process and I was just told it would be refunded. Today the refund comes through and it's R400 less and I'm told this is because of the R400 promo received on the purchase. So basically I've been charged a delivery fee for an undelivered item?? This translates to me literally walking into a Mr Price store and just giving them money and walk out because I've incurred a cost for something I did not receive WOW hey, just WOW. Never again will you see me purchasing again. Your customer service sucks because if there is going to be a cost or deduction to my refund then I should have been advised accordingly and been given the option of a voucher then rather than have to learn of this when I queried after having received a less refund.