By manually filtering in the database you can remove these fraud transactions if they all came at the same time by filtering the name of the order for invoices and the transactions Value exactly if it is not the same as anything else you have in store and setting rows to 500 or higher and selecting all and deleting.
You're at hand for modifying your database, I would backup in case of any accidental deletions, I've already accidentally deleted 1 real transactions during this time but modify if you would like these removed and use anti-fraud rules.
MinerSpark's post in Mass delete/remove Invoice+transactions was marked as the answer