List Spammed

Have had the list set up and working find for about a month now, but starting Sunday the list was flooded with garbage signups. The data being sent is a first name, a random string of characters in the surname field and an email address which may or may not be authentic.

The data is processed by the database and the list extended with these names but what is curious is that the attack is not being done from our website. We had something like a thousand list sign ups in 6 hours on Sunday but only a handful of visits to the website.

I turned the list off and stopped sign ups on Sunday evening but when I put it back on again the attack continued.

Anyone any ideas what could be going on? The website is https://www.sheselectricmovie.com/