When you block someone in Gmail, it does not prevent them from sending you emails. Instead, their sent emails are automatically redirected to your spam folder, where they will remain for 30 days before being deleted.
To completely stop receiving emails from a blocked sender, you will need to create an additional filter that automatically deletes incoming emails from that sender.

In this article, I will provide you with step-by-step instructions on how to create filters that will prevent blocked emails from entering your inbox.
How To Stop Blocked Emails From Coming Through In Gmail?
1 – Go to your Gmail inbox.
2 – Click on the gear icon in the top right corner of the page.
3 – Click on the see all settings button.
4 – Go to the “Filters and blocked addresses” tab.
5 – Click on the “Create a new filter” link
6 – Enter the email address of the person that you blocked in the “from” field.
7 – Enter your email address in the “to” field.
8 – Click on the “Create filter” button
9 – On the next page that asks “When a message is an exact match for your search criteria” select the “delete it” option.
10 – Click on the “Create filter” button again.
Now that you have created this filter, all future emails from the blocked sender will automatically be deleted. However, you will need to manually delete all emails from the blocked sender that you received before creating this filter.