Even on reverse it goes forward? Or does the vehicle stay locked in place? How does the car behave in park? Does it act like it wants to move forward but is stuck on something? When my FWD clutch burnt up and welded together it would go forward on neutral but on reverse the car would just stay still... I guess it wanted to go forward and back at the same time... In park the the car wanted to move forward also but the parking pawl was keeping it still. If these are not your symptoms I would also suspect something else... start with the basics like checking if the shifter rod is still in place. It might have come undone and the transmission is on "drive" mode no matter where you put the shifter.
