>>105612730 (OP)Reinstall the OS, and select erase disk and install.
Assuming your original setup was with disk encryption, that will throw away its keys as well, making all data unrecoverable.
If you did not encryption originally, you can shred -n 3 data you want unrecoverable, before reinstalling OS, or with the usb live boot of your OS before reinstalling, find the underlining disk and shred it entirely:
sudo shred -n 3 /dev/_yourdisk_
Then reinstall on to that disk