Poor Customer Experience

I brought in my car in December as it had a malfunction, I was told by my service consultant that a software upgrade was done and it was sorted, needless to say she was not being honest, I am still experiencing the same problem which makes it incredibly challenging to drive the vehicle. I've called into Sandown Motors in Sandton to speak to this particular consultant so that I can get this driving issue resolved but she doesn't return my calls which begs the question why?? This is unacceptable Mercedes, this is not an experience that should be associated with your brand. I need my car fixed because driving it is now a huge risk.