double payment unrefunded

I bought a few items at Mr Price Woodmead, i was billed double. The cashier and the manager claimed that i will be refunded in 24hours. This was last Thursday. Monday 9th i check my statement and INDEED i have not been refunded. Now to my inconvenience they say i must go to the atore to fix this. But i told them to fix it on Thursday when i was still at the store. Now i must cancel my business trip for the store's incompetence go sort out my koney? How can the store not have an email address in 2015? I refuse to go back to the store i just need my money refunded like they said it will be!!!