Daemon-Byte they seem unable to implement any method to stop spam bots on the contact form and he was getting overwhelmed with spam.
If they don’t do anything, they’ll probably eventually end up on a spam blacklist…
Filters only apply to newly-received emails; they don’t apply to emails that have already been delivered to the inbox. Your filter configuration looks fine, so any new emails that match the filter should be moved to the right folder.
Do note that moving emails to the “Junk” folder trains the spam filter, so it’s likely that all emails from the contact form (even legitimate ones) will start to be marked as spam if you do that. You may want to create a new folder just for the bad contact form emails, or get the webshop to properly implement spam filtering on the form.