How can I reduce the humidity level in my basement?
An assortment of thoughts which may or may not be applicable to your situation:

In general, larger capacity units are more efficient than smaller capacity units, according to Consumer Reports. They suggest buying a 70 even you don't think you need it.

If you're using the built-in bucket, the dehumidifier stops whenever that becomes full. You have to empty it as frequently as necessary... or set up the unit to drain into a sink or otherwise move the water out of your house automatically. (Mine has been draining into a pump which in turn empties into the washing-machine drain.)

If you have water coming in as fast as the dehumidifier can pull it out, you won't make progress. How well sealed is that basement? 

Make sure you have allowed enough air circulation around the dehumidifier and into the rest of the basement.

Dehumidifiers are somewhat notorious for recalls. If you really think yours isn't working properly, you might want to check with the manufacturer to see if there's a recall that hasn't been announced yet.. (The last two I've owned were both recalled; the first seemed to be working OK for me, the second was clearly bad from the moment I turned it on).

Good luck.