Gearbox and Diff Doctor Horrendous Service

I had a Diff on my BMW 320i Manual 2012 model replaced on the 9 December 2020. Twice in the same December had to return to the workshop as the replacement Diff was leaking. Noted the warranty on the Diff i was informed is 6 months. Around August 2021, I noticed that the Diff was noisy again albeit at low volumes. As months went by, the noise got worse. Only this December when I was having my tyres sorted I went under my car, only to discover that the Diff has been leaking from where the Diff joins the Prop Shaft. I then got in touch with the workshop that replaced my Diff, specifically looking to speak to the manager who had attended to my car when I was not satisfied when there were initial leakes from the newly replaced Diff. I was then informed that the Manager Mr. Costa was on holiday and they could not help. I then discovered that there had been a new branch opened near me, in Randburg. I got in touch with them(Randburg Branch) only to discover is the same Manager Costa, as one from the Doornfontein Branch. I was then informed that I was to pay an additional R12000 to repair an issue on a refurbished Diff I paid R8 000 less than a year ago. This manager cannot be reached on his listed mobile number yet the Randburg Branch is in constant communication with him on the same number. I was later informed to send him a WhatsApp text that is yet to be responded/attended to. I would not recommend anyone to this guys.