I keep getting some unwanted email from
firstname.lastname@example.org at least 20 emails/day. I tried to unsubscribe but no luck in that. I tried to all the way I can't block at all. Finally, I decided to move all mail to spam. Is there any way to stop this?
Gmail allows you to block email addresses. Open the email in Gmail and click the down arrow on the right of the screen, there is an option to block "spammer" (where the spammer is the name of the sender). This will send all future mail from that address to spam.
Alternatively, if you don't even want to send the mail to spam, you could create a filter in the settings under 'Filters and Blocked Addresses' for mail from the spammers address and then in the filter select 'delete it'.