"choise wrong file for downgrade" -- that can happen when using directions that aren't being maintained. Sorry to hear that.
You should still be able to flash the correct firmware version and thereby fix your Kindle by following the serial jailbreak instructions, and while you have access to the diags partition, overwriting the main partition with the
correct rootfs.img
rootfs.img can be extracted from the update file, using
KindleTool.