Bad service

We bought a part from them to install. They charged us labor for installation. On the day the car was taken to them to install the part they did another diagnose and told us the part we bought is not the problem we had to buy another part. Story short car is still standing they want to charge us more money to diagnose and get another part. All we want is just for them to install that first part that we initially bought. Contacted Volvo SA they never responded