Vex robot controller only one side working

we are building a robot using the controller I had program it correctly and all and all the parts are working but when I try to drive my robot . only the left side work at all time, my teacher try to help but is also confused. We built a 2 wheel robot trying to use the tank drive(Ch2 and 3) we try everything from switching controllers, switching ports, switching channels, switching parts and switching cortexs but nothing works. Everytime I try to drive no matter what channel Im getting to use only the left side while work(example: program lmotor with channel 2 and rmotor with channel 3) but only left side drive and right side don’t drive. I debug it and both motors are working all batteries are just charged. So I try switching the channels(lmotor channel 3 and rmotor channel 2) still only left motor works. Teachers suggest controller update did it nothing different. We thought maybe the cortex was broken or controller switch it out same problem. Please help. Thx

post the code you are using.

Try switching the motors or check the code.