Stop receiving Strong 8K emails
One short message does it.
Ask once, by email
Write to support@4kzone.site from the address you want removed and say so in a line; the order number helps if you have it. The address is taken off and you receive one confirmation.
Emails about a line you have paid for, the account password, the subscription details and the reminder before it runs out, are part of the service and continue for as long as the line is active.