comments turned off but have been comment spammed

My website has had comments turned off from the very beginning. It has never opperated as a blog. In the last 6 weeks 1000’s of comments have arrived – mainly related to preteen porn. I have deleted the database and restored from a backup taken before this started and changed passwords multiple times but they still arrive. I have akismit activated so it is a matter of daily emptying the spam but would really like to find a way to remove their access to my site. Help please! I have not included a link to my site as (fortunately) these comments are not viewable except on the dashboard.