Poor customer service

My vehicle is 4 years old and was due for a major service. Contacted the Car Care Clinic and got a quote for the work. Car was booked in on the 28th of October. When my partner dropped the vehicle he was told that not only did it need a major service but a whole lot of other work which would push the price up to well over 17k. Spoke to Shahied and agreed to the service plus an engine flush. The vehicle was collected, we didn't receive a diagnostic report with the job card and invoice. Come November, I call back to book in for the first part of work post service per my quote #QU100164 as prices indicated are valid for 90 days. Car is booked in for Friday 28th of November to have the fuel line cleaned, the throttle body cleaned, cabin filter done, engine sump resealed as well as the sealant. This costs another 2.2k and some change. Between the major service and the second body of work the car is intermittently not wanting to start. Had to be kick started over half a dozen times. I call to ask for Shahied only to find he was asked to leave. Spoke to Verity and explained that the car was not problematic before it was booked in for the service in October. I requested the full diagnostic report that was meant to be provided. Not sure how many points their check is but nowhere on my quote nor the diagnostic report was any indication given that the battery was checked, let alone a problem. Sent an email to express my dissatisfaction on Tuesday the 10th of December and got no response. Sent them a message via WhatsApp the next day to indicate that I had no feedback and could somebody please respond. I was told that the manager [Regan] would call me, which he did. I expressed my unhappiness while explaining my situation, he indicated that I could bring the vehicle back for them to check. Took the car in today. While the car was being checked I asked Verity if she could update the contact details on my account. Her colleague very loudly and rudely said that it can't be done if the invoice is already printed. A whole new account must be created with the new information. Shocking to say the least. I then take a walk to the workshop and Regan proceeds to tell me what I already know.....that my battery is FLAT. When I asked what could be done he hops on the phone and comes back to tell me that the battery is going to cost 1.2k and they will change it free of charge. At this point I went ballistic and kept re-iterating that the diagnostic check wasn't done correctly. They refused to budge. Eventually telling me that if I bring it in for something else i.e. an aircon regas they would fit a battery free of charge. I REFUSE TO PAY FOR SOMETHING THAT SHOULD HAVE BEEN IDENTIFIED 2 MONTHS AGO!! And then the attitude of one of the workshop staff was that nothing in this life is for free. I am a paying customer who has paperwork to prove that you didn't do your job properly and now I'm expected to fork out almost R1300 to buy a battery that you should have checked when the car was serviced? No!!! Long story short, they refused to do anything to assist on account of an employee who is no longer there. I left with a flat battery and unhappy. Car Care Clinic has lost a customer for good. Never ever, again!!