Voice Memos and Notes during Erase all Content and Settings.

Hi there. I have to "Erase all content and settings" to sell my phone, but can't see anywhere that this also deletes voice memos and notes. I have gone through and manually deleted them (including deleting them from the "deleted" folders), but I just want to ensure that after the "Erase all content and settings" has been pushed, they can not be recovered at all. From reading online I can see that photos, messages, credit card data etc., all gets deleted, but can see no mention of voice memos and notes. I want to ensure they are entirely deleted and not (at all) recoverable. Thank you.