LuLu Hypermarket review: faulty billing

Yesterday 2nd Jan 2020, I had been to Lulu Hypermarket Ramli Mall, Bahrain. The 50% discount offer on garments, shoes, bags etc was going on which was ending on 4th Jan. I bought some garment items worth 36.9 BD which was eligible for 50% discount as advertised by Lulu.In addition to this we bought 7.8 BD ( socks) which weren't eligible for discount. The check out counter guy couldn't understand the discount billing properly and gave us only discount worth 12.4 BD instead of 18.450BD, which was a loss of nearly 6BD for us. Despite repeated requests, the checkout counter staff couldn't understand this simple math and we didn't get 50% discount as promised.
Ref
1.Receipt # 303411 dt 2/1/2020.
2. Receipt # 303412 dt 2/1/2020 served by 1421754.
Please arrange to refund BD 6 to us.