Unfair treatment

On the 28th I purchased a Samsung phone via online at game using my rcs game card. The purchase order was 3299.00 and I then on the same day cancelled the order via rcs contact centre. The order was cancelled however I was refunded with the incorrect amount of 2865.65 instead of 3299.00 in my rcs game card. I then contacted their contact centre to inform them about the incorrect amount credited. I was told to send an email to their merchant services which I did and todate they have not responded to my email and corrected the amount. This is unfair treatment to me as their customer and I want the refund amount to be corrected.