I know different cars have different methods, Are you sure you arent supposed to push down on the stick? I know I had to do that in a Maserati to get into reverse.
My MGB was just an over to the side past the pressure.
other cars I have seen you have to pull up on it.
Sometimes it helps to shift into first then to second and then try reverse, sometimes it helps to shift to first then try reverse, and sometimes it helps to move the car in first just a touch then try reverse.
I would think one of those should help, unless there is a mechanical problem with it.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.