As bad as that sounds, it could be as simple as a worn bushing which would cause the cable to come loose from the linkage. It may have also been a broken shifter cable. So the first step would be to verify that you are actually shifting the transmission. If your cable and shifter check out, now you would look at the transmission by checking fluid level and the condition of the different transmission components. If nothing obvious is seen then your problem would most likely be internal to the transmission. I recommend having a mechanic, such as one from YourMechanic, inspect your vehicle’s transmission to see what needs to be repaired.