not allowing comments

Hello,

I have thousands of spam comments on my website. My host told me that if I was able to turn off commenting completely, and add captcha plugin (which I did), they would reduce cost of my repair by 50%.

I went to settings and discussion and unclicked “allow people to post comments on new articles” and updated, but then the check mark was back next to the box. Tried multiple times and it stayed that way.

Then went to all posts, selected all, edit, and “do not allow comments” and clicked update … and i went back in and the “do not allow” was not selected.

Any thoughts on this?

Thanks
Pete