Users Registering With No Registration Plugin

Hi

I have recently been receiving emails entitled ‘[The Weekender] New User Registration’ from my blog – https://theweekendersa.com.

We recently moved from .com to .org, but have only installed a contact form plugin in which, when I test, sends an email with the subject line ‘Car Insurance Lead’ – as I have set it to say this. The only other place users are able to fill in their details is on the ‘Advertise’ page but. again, this email comes through with ‘advertise’ in the subject line.

So I have no idea where these users are filling in their details?

Please help.