Your vehicle's battery and alternator usually don't give up in just three years. Have you installed any aftermarket accessories? Something might be draining battery power, even after the vehicle has been turned off, commonly known as parasitic drain. Ask the service centre to thoroughly check each fuse to identify the solution.
Since you have already spent on repairs, and assuming the problem has been resolved, you should keep the vehicle and continue using it. Selling the car will not only result in a financial loss, but you will also have to put in more money to purchase a replacement vehicle.

