Poor Service

I bought a BMW 320d for the second hand dealer. From the fist day that I have bought the car I noticed some problems with the vehicle. I notified the dealer of the problems but only some were fixed. The one specific problem the sales person who sold me the car said that its normal its not a problem. after getting a professional opinion it was confirmed that indeed it was a major problem. I notified the dealer and he agreed to have it fixed. I even offered the dealer to make use of my motor vehicle plan to help them with cost. It is now six months later and the problem is not fixed yet. I have mailed and messaged the dealer but now he ignores me. The service was excellent but the after sales service is beyond poor.