Not willing to refund for a battery

Purchased a Samsung S3mini battery from Cell C in Centuion Mall on 27/8/2015. The batery inside the pack was not a Samsung S3mini battery. On 30/8 my husband took the battery back to the store, they had no other stock and informed us that they will have stock on the 2/9. I went back to the store on 10/9 and they still do not have stock. I requested that they refund me to enable me to go and buy a battery from another retailer. They refused to refund me and advised that they can get me another battery from the other store in the mall, but it will cost me an additional R 151 ....This is ridiculous....do they really expect me to pay more than double for the battery in addition to the petrol and parking I used to return/collect the battery.