Poor customer service

I have a 2016 Opel Astra Turbo. I took my car in for its 60 000 km service. This was actually the first time I did not have the endless calls to follow up how far the service is but that where the positive experience ended. When I received the car back it was working fine. Three days later my troubles started. The car started to give various warnings and struggle to start until it eventually refuse to start. I phoned Opel road side assist and the car was towed to Reeds Bellville in Voortrekker rd. They tested the car and told me there is nothing wrong and also took the car to Battery centre to run a test on the problem. Late afternoon they told me they cant find the fault and I must take photos and video clips as proof that the problems is still there. I did this for more than a week and then I made another booking to have the car looked at. They now told me the battery needs to be replaced but could not really give me answer if it will solve the problem. The car has been once again 2 days with them and it seems they are just utterly clueless on how to fix the problem. I use to be huge Opel fan but can honestly say this is the last time I will ever buy any Opel product again.