Sending spam from a site on Prestashop

The online store was created on CMS Prestashop 1.6.0.14

Last week the outbound message limit began to be consumed rapidly

Although there are no mailings from the site

We tried to protect the contact page and the page with the message form from bots

But the limit continues to be consumed

We need to find a reason and protect site from being used by bots or intruders.