Very Unsatisfied

I took in my car to Mercedes Benz Constantia Kloof a few weeks back because the engine light came on and it kept going into limp mode. The service adviser then told me to fix the car would be +- R30000.00 - I had warranty so only paid 40% of the amount which is still a hefty amount of around R11000.00. When I went to pick up the car (after they advised me the car is fixed) it was not even a day and the car went into limp mode again (the same problem) I called the service adviser and took the car back in. Then went to pick it up - the problem persisted for about 3 times we took it in and it kept coming back with the same problem. I then filed a complaint and wanted to know what is going on.

And then received this message from them.

"Good afternoon Please find attached quote for the engine control unit to be replaced. The engine light and limp mode function goes hand in hand. However, the one can work without the other one. There is multiple functions for the engine light and even after the repair the warning light can go on again for something else. "

The new quote is also R29482.70

I'm so unsatisfied. We paid to get something fixed only to be told " it was not that it could be anything" So do I need to pay R30000.00 every time they don't fix the correct thing.