Hi Lindsey, here the response I received from my host.
"I understand your concern and the need to identify the origin IP address from the access log. However, I regret to inform you that our team is unable to assist with this specific request.
While knowing the IP address from which the account was registered might seem helpful, it's important to understand that the core issue here isn't the location from which the action was performed, but rather the method used to do so.
In light of this, I would strongly recommend seeking the expertise of a professional web developer. They would be able to thoroughly investigate any potential security flaws that may have allowed for such account registrations and make the necessary adjustments to your application to prevent such occurrences in the future.
Please note that this situation falls outside the scope of our hosting-related responsibilities. If you suspect that your website may be compromised by malware, it would be best to consult with a malware removal specialist.
I understand that this may not be the answer you were hoping for, and I truly empathize with your situation. However, I trust that you understand our limitations in this regard."
I have checked my website activity log and I have blocked some IP addresses used by the user. But he keeps registering on my website. My plugins are up-to-date, so I don't know where this problem is coming from.