First, locate the g/box dipstick. There will be a hot and cold marker on it. Check that the level for the cold check is actually registering before going any further with checks, if not, add fluid until it does.
Then after a short drive to get the box and fluid hot, carry out the hot check as instructed. It may sound daft but the level when hot will become apparent when you look at it.
The correct level may be an issue and certainly check it but i'd be inclined to do a diagnostic check as it sounds more like a faulty solenoid problem.
How long has it been like this, were there any symptoms prior to this fault ?