made me buy wrong parts and still with a problem

I took my vehicle CN 47 TN GP for service at Zambezi auto BMW two months back and have some work done on the left front door and was all paid for and also requested for a heater to be checked as it was not working and I was told that it is the valve that is not working and I believed that as I asked them to check as they are the ones who built this vehicle they would be able to fix the problem but to my surprise when I paid for the part and labour and took the vehicle to them I was told they are not happy with the way it is not warming up enough and they needed to strip and more time which I gladly gave them and later I was told that a clmate control component is not working or something and I was advised to get another one and theirs was R16000 and the service advisor who was assisting me advised me to get it somewhere else which I did with the fraction of the price but when I gave it to them to istall they told me later that it is not warming again and again I was told to get the component with the same numbers which I went out and get and yet again it was not working so they took another component from another car and installed it there and they called me and I went there and f