I have understood the requirements, The possible cause of issue is web crawling attack. The possible solution to problem is integration on captcha on contact us form including all other forms that is accessible without authentication. We would also recommend to integrate CSRF and XSRF token authentication on such forms.
I am a new start up company working with objective to deal in delivering quality Web solutions using Magento, PHP, Laravel, CI, Angular.JS, Node.JS, WordPress, AWS etc. We first understand business aspect and problem statement and after analyzing thoroughly we propose solution which best suite with your requirement. A chance to work with you on your project will ensure a successful and timely delivery. Let's Connect.
Best,