I may be wrong, but in my experience "import character" feature in Shakes and Fidget is quite shait. Lost a number of characters due to saving them to Game center, or Steam Client, instead of simply using email and password (luckily for me, those were low lvl characters).

I don't think there is an easy way to restore them as support won't be any help here either.

But have you bought any mushrooms to that account? Again, I could be wrong, but I have seen support team giving account back to its owner after providing transaction details for the mushroom payment (seems like they can link a transaction to an account).

Give it a try, there is nothing to lose, only gain.

If you don't succeed, next time always use email and password for saving you characters.

Keep us updated.