Mechanic Changed My Gearbox Without Proper Diagnosis – Now What?

Hey everyone, I currently have an issue with my 2015 Kia Rio (automatic) where it wouldn’t shift past 3rd gear and was revving too high on the freeway. I took it to the first workshop, and they told me I needed to replace the gearbox.

Since they were taking too long to source a part, I went to another mechanic, told him what the first workshop said, and he immediately found a second-hand gearbox with 40,000 kms on it. I agreed to the swap, assuming he would confirm the issue before replacing it.

Today, I went back to test the car after the repair, and the same problem remains. The mechanic’s response? "You told me to change the gearbox, so I did." Now he says he will check further and let me know what can be done.

At this point, I feel like the gearbox may not have been the real issue, and I might have paid for nothing. Now I’m worried that he’ll say something else is wrong and ask for thousands more.

For those who’ve been in similar situations:

• What should I say or do next to make sure he actually fixes the problem and doesn’t charge me even more for another unnecessary repair?
• Do I have any consumer rights in this case?
• How can I make sure this gets fixed without throwing more money at unnecessary repairs??

Any advice or similar experiences would be really helpful! Thanks in advance.