My basement sewege ejector pump started humming a couple days ago and I can now smell the sewege. I have unplugged and plugged it back in but the humming does not stop.

The first thing I would look for is a stuck float.

Sounds like 2 problems here. If you are getting a sewage smell the lid seal or the vent is no longer sealed air tight. While it is humming flush the toilet and drain any other fixture that drains to this pump. Can you hear the water flush up the pipe? I'm with Harold, stick float in the down position

There is an electric switch in these pumps. I had one and every 10 years or so the switch needed to be replaced. After the 3rd time I put in a new pump, hoping that it had better parts. But it is most likely the nature of the beast's environment - being really damp, which can make electric parts corrode.
To troubleshoot a thing like this you sometimes have to take a piece of wire and bypass the switch (then plug it in and see if it works).
If you can take it apart you'll be able to go to an electric parts shop and replace the switch.