If they’re emails (received via your email program) then Akismet probably never seen them. Your email program will need to deal with them.

If they’re feedback received on your website then you need to look at whatever feedback method you are using to receive these and deal with them appropriately.

If they are comments and Akismet doesn’t recognize them as spam then you need to mark them as spam and then delete.

If you can identify the spammer by IP address or CIDR range then you can block them via htaccess.

You can sometimes locate country-specific lists of IPs to ban most all users from that area.

Sometimes the bad actor will trigger firewalls so running something like WordFence might help you slightly.

Hope something here helps.