Bad service from Volvo Bryanston

I bought c30 Volvo 2010 for 135 000 cash, from Volvo Bryanston, I experienced a problem with it within a week then I contacted the salesman immediately and was requested to return it for some test so that it can be fixed, It was diagnosed but his manager said he's not responsible for that since the car is old, I'm the one responsible for the costs since the car is still moving, the problem is a minor and isn't under warranty. Then I opted for refund since I can't afford paying for so much for something that I'm not happy with and his response was I'm sorry ma'am I cannot cancel the deal, ull just have to take the car as it is because your complain is just a minor. It's 3 weeks now they still have the car with them and I have paid cash.