Here are my problems, recently I and my users are getting this error while posting comments.

Error message: "You are posting comments too quickly. Slow down" Not just it, I can't see comments but count is increasing in dashboard. Also people can't contact me via contact form page, which also show error.

After this I had taken this actions:

1. Deactivated theme and plugins.

2. Replaced with native theme and no plugins, but did not solved the issue.

3. Upgraded WordPress, Apache, PHP, MySQL etc.

4. Upgraded my theme and plugins.

5. Checked my server DNS and other settings.

6. Shutdown cloudflare.

Here is my doubt, I believe wordpress come with by default anti spam or aksimat moduls. Who some how triggered by flood of spam comments. Or some how firewall got activated. I dont know further stuff !
Here is my website link: https://www.planetradiators.co.uk/product/oval-panel-single-anthracite-400-x-420mm/

please give me accurate information for solving this issue