Wondering which method you used to block the email... Apple Support's online articles (links below) may help find what works for you:
(1) Block phone numbers, contacts, and emails on your iPhone or iPad - Apple Support
Eg: says:Mail
"From the Mail app, open the email that has the contact that you want to block,
then tap the contact at the top. Tap Block this Contact
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(2) "You can also add an email address directly to your Blocked Contacts list in the Settings app.
Add the number or email address that you want to block to your Contacts.
says:
"For email addresses, go to Settings > Mail > Blocked > Add New.
Select the contact that you want to block."
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(3) Flag or block emails in Mail on iPhone - Apple Support
Eg: says:
"Block email from specified senders
You can block an email address to prevent a particular sender from emailing you in the future.
Tap their email address, then select Block this Contact".
All the best :-)