Dissatisfaction about the service

I went to bluff tyres at Pinetown to install 4 Bridgestone tyres, when I arrived they said they have only 2 Bridgestone tyres in their branch but they will get the other 2 from another branch. They asked me to pay in advance so that they can collect the other 2 tyres. I paid for all four tyres .On the following day I called them to check if they have all 4 tyres. They said they have all 4. To my surprise when I arrived at their branch they installed other brand of tyres in my car. I told them that I paid for 4 Bridgestone and I asked them to remove the tyres they have installed and refund me my money. They removed the tyres but they did not refund me.Its more than one month now Bluff tyres has not refunded me. I phone them weekly, requesting my refund I’m so frustrated I really don’t know why are they not refunding me.