Andy said:An imposture has usurped my name. I don't blame them.
usurp:to take someone else's power, position, job etc when you do not have the right to.
It seems to me that the subject of the first sentence, an imposture, should be someone, rather than something. What's more, the second sentence's object also implies that the first sentence's subject is someone rather than something, despite 'them' having been used instead of 'him'.
Maybe you are indeed no imposter. So I'll retract what I had posted earlier about that.
But the mystery of who the imposter is remains unsolved!