Overcharged - Consumer Complaint for MAKRO - Head Office

I purchased 3 shirts from Makro Carnival on Thursday. I was charged for 4 shirts as one of them was duplicated. I raised this with Customer Care but was informed I must go back to the store to sort it out. This is not acceptable. I am a pensioner and it is a 50 km round trip to the store. Please will you sort this out online. I can email copies of the till slip and invoice. Tony Medway.