Disappointing and Bad service from Store Manager at Edgars Festival Mall.

I am very disappointed in the service I have received from the Store manager at Festival Mall, more like no service at all. I won a shopping voucher in a store competition in May, the head office sent my voucher but the store reversed a portion of the amount as they didnt balance on their side. I didnt finish all the money I won and they still owe me 20% of the amount. Until today I am still waiting for my voucher, if I dont call they dont call me back. When I go in store I get excuses. This is such a bad service from someone who messed up but cannot own up to their mistakes. 3 months down the line, still no decency to give me a proper way forward so that I can forget about it and move on. They have turned an awesome moment into a disappointment.