Worst company and service ever!!

Good day, I am having the worst service delivery with this company fixing my car. It's been with them for 5 months now and I had to pay 50% deposit up front after fault finding for them to continue fixing it. I paid and the first part was quick but then came all the excuses after excess why its not fixed het. I send it in for a mechatronic repair and ended up overhauling the gearbox as well, then the gearbox lost its memory to shift so they had to reprogram the gearbox. Which they have been doing for over 2 months now driving and setting it just to tell me that it lost memory due to outdated software, which I believe is total bull!! So my car is there now for 5 months and I gave them an ultimatum that I will be collecting it in 2 weeks time whether its fixed or not and if not I will not pay a cent more! . Any other advice or help would be appreciated.