Queuing for 30 minutes to refund overcharge of special advertised openly.

On Tuesday I made a purchase at the Game store in Trade Route Mall Lenasia. One of the items purchases was a special advertised in store and online, on my slip however It shows that I was charged the normal price for these items. I queried this with the cashier who advised I should speak to customer services. The customer services desk had 2 availaible desks with only one person working, at the time I joined the queue for customer services there was one person at the desk being assisted and one person in the queue. I waited more than 30 minutes to be asissted, during this time I asked 3 staff members to assist me. I was advised that only customer services can assist me with refunding my items after which I had to go back to a cashier to cash the items on the special price. I asked if there is anyone to assist at the customer service desk as we are waiting a while to be assisted and there is only one person attending to the queue, I was advised that there is only one person to work on the customer service desk and I had no choice but to wait for her to attend to me. I had to pick up my kids from school and had no choice but to leave without assistance. Making me queue for 30+ minutes to rectify a mistake I did not make is appauling and I am still not compenstated for my time wasted or being charge incorrectly for an advertised special. I have to now resorte to emails which results in administration for me to get assistance with rectifying a mistake I did not cause. Please rectify this