How to not have an image in a facebook share
First of all try investigating URL you are sharing on Facebook Debugger:
https://developers.facebook.com/tools/debug/

If you are not providing og:image meta tag, Facebook will try to get the best matching one, I guess those AD images in your case.

Unfortunately there is no way you could not provide an image, you could try with empty og:image meta tag, but I don't think this would work.

It would be best if you provide an image anyway. Here are some hints:
https://developers.facebook.com/docs/sharing/webmasters#images