Protect your forms with a captcha : easy to setup, it contains multiple checks to stop the robots
Mathematical check
Ask your visitor to make a small calculation. As this is a visual check rendered by an image, a basic robot will not be able to read it
Time check
Setup the time you think your visitor shall spend before sending the form, if it is sent too fast, it's a robot
Hidden field check
This is a honeypot, no human will fill it, so if it is checked, it's a robot
No hidden cost, you can use it as many time as you want.
Read more https://extensions.joomla.org/browse/new/extension/access-a-security/captcha-ck
