I must say the customer service stinks

I had 2 same items in cart but with different sizes. When I ordered I first deleted the one with the smaller size. For some reason when I finished the order, I noticed it was the wrong one. I had a 6% discount coupon because it was the first time buying on Leroy Merlin. I contacted Leroy Merlin to cancel the order, and I asked if I order the correct item if I will still have the 6% coupon and I was told no I will not have it. If it such a problem to still give the coupon then then I must say the customer service stinks.