Hi Fran43,
For help with ensuring the contact or address is blocked, check the settings with the steps found in the article here: Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch - Apple Support
If this only occurs with a messages from a third-party email account, check with your provider for any additional settings to block a contact.
If this is an iCloud mail account, and you're also seeing the option "Move to Trash" is enabled when navigating to Settings > Mail > Blocked Sender Options, reach out to Apple Support to further assist.
Contact - Official Apple Support
Contact Apple for support and service - Apple Support
Best.