Phone not repaired and My money GONE!

On 29/07/2024 I took my phone in for repairs in the store at Mall of Africa. I was helped by a technician by the name Lebogang Modiko. I gave him the phone to diagnose what the issue was. He took a look at the phone, and he advised that the phone needs a screen replacement and that I have to pay a full amount of R1850. He reassured me that the phone will be fixed that's why I have to pay the full amount. He said I should come and collect the phone in 3 days. Till today my phone is not fixed. He is now telling me about additional parts that were not mentioned in the initial quote. He says I need to pay for the mainboard of the phone which he did not mention in the original quote. He say's the mainboard was faulty from the beginning which I disagree with because my phone was switching on when I took it in and now it doesn't switch on instantly. I have to keep trying to switch it on and it will finally switch on after a lot of tries and still switch off again a few minutes later. I could have taken my phone to a non-Samsung store to get it fixed cheaper, but I trusted that Samsung would do the best job. but instead left me without a phone and my R1850 gone just like that. I have been to the store back and forth and the gentle man kept sending me back without a phone, and each time made me feel like I had not paid for his services as he would be rude and tell me off.