Hello and welcome to just answer. This is a known problem with the 300C and Dodge Chargers. There is a lever/tab in the shifter mechanism that breaks and causes this. Now this may be covered under a recall or it may not. The shifter will need to be replaced or repaired by the dealer. Call them up and give you the VIN # XXXXX the vehicle. They will then be able to tell you if this is covered under the recall or not. Hopefully your's is.
I hope this information helps, and let me know if you need further assistance with this.