umm.... pre-quals w/ LC or Prosper are SP's. you have to go out of your way to actually apply and get a HP.
just dispute it on the corresponding CR and say you didn't apply.
Just so that we're all on the same page. You were actually alerted of a hard pull via your monitoring service, or are you just assuming you received a HP based on the denial email you received? I too received the denial email without applying, but there was no hard pull. I recently also signed up for Credit Sesame, though I didn't look for a pre-qual on their site at all. Very disturbing whether it's a HP or not.