When did you create the contact form? With what version of Form Builder?
My first question would rather be:
When the form is being accessed like this, are you getting emails through through?
if not, then as the host tech said, they may be trying to find a vulnerability, but are not succeeding.
that log shows that there are 3 IP addresses accessing the page:
you could use HTAccess to prevent access to your site from those IP's: