Overcharged

I bought clothes from Jet at The Glen Mall few weeks ago and was overcharged by double payment. When I called them as I stay in Mpumalanga and they said I must go to my nearest Jet and I did that but unfortunately they told me they won't be able to help me as it will become a loss to their store. Now I called The Glen Mall Jet again and gave them feedback but they told me I have to go there. My problem is that I might go to Joburg even next year, I'm not a regular there and when/if I go there I'll be using my own time and petrol to go there for a mistake they made. I WANT MY MONEY BACK