Have you used Kongregate in the past or logged in to another account of yours by mistake? Have you used any hacks to increase your score?
If you have used Kongregate in the past, it has a "merge accounts" button or something like this iirc. It is possible you have merged your account by accident with another account or something similar. Or, like kaempfer13 says, it's possible that you automatically log into a different account there.
Right now, I am afraid that your account may actually have been hacked. There were similar cases like yours in the past, but I don't know any of these cases to be ever solved, especially with the EtG developer being inactive for so long.
Good luck anyway.