Toyota Belta 2006 transmission

Hi everyone
I am from Guyana, which is situated in South America. I bought the Toyota Belta here in my county. When I bought the car, I visited the mechanic for overall checkup of the car to ensure that the car has no issues and is working properly. The mechanic checked the car thoroughly and said, yes, the car is in working condition. After a year, now I am experiencing a transmission issue in my car and the mechanic told me that he never checked the transmission oil of the car. This is the reason why on acceleration, the car will jerk and then will move ahead. The car is now moving hardly. Again I went to the mechanic to check the car again and asked him for the car attention to find out the actual issue due to which the car is behaving like this. The mechanic asked me to replace the transmission oil and suggested I use the Shell Dextron DIII. I did so and again the car issue was not resolved and started creating more problems. Then I visited another mechanic and he asked me to use CVT oil, which is the correct oil for the transmission of the engine. After doing this, the reverse gear of the car stopped working and is not reversing now. While driving the car I noticed that the car is jerking. But it is driving in neutral mode. Kindly, can anyone help me in this situation? What should I do next? The car specs are mentioned as under. If I go for second-hand good transmission then at which price will it be available? o r should I buy a new transmission for my car? and from where can I purchase the transmission? Please guide me in this regard o fix the issue with my car.
production period: 11/2005
catalog code: 141170
complication: SCP92-BEXNK
frame number: SCP92-1000599
engine: 2SZFE
grade: x
trans: ATM
options: cvfc
trans# k410-D3A579
model: DBA-SCP92-BEXNK