Miss diagnoses

I took my LDV to Auto Box because of a strange noise coming from the rear of my LDV. They diagnosed the problem as the bearings on the diff where the driveshafts exit the diff. I took my vehicle in and constantly had to phone them for feedback after they promised to keep me informed. After taking out the diff it was determined that they made the wrong diagnoses, it was only the center bearing on the prop shaft that was faulty and that the diff was in good order. Since the diff was removed and the vehicle has high mileage they convinced me to replace the two bearings they initially thought was damaged in any case to which I agreed. When I got my vehicle back there was a terrible humming noise from the diff which was not there before. I took my LDV back to them and they told me it was because they re[placed the bearings and that the noise will go away in time. It did not and I went back to them again only to be told that they take no responsibility and again told me it will get better in time. It is now a year and 8000km later and the noise is worse than ever. I will not recommend or trust these people ever again.