'different then' is one of the clues in online written communication that the writer speaks American English (with some confusion), 'different than' is 'correct' american english (though seems odd to me as an english english [or just simply: english] speaker), 'different to' is, I believe, more common in english english but not american english, and 'different from' is probably the most correct and universal formulation, and I use the word 'correct' with all the usual caveats when applied to language.