I don't stand out from others who reacted to your proposal, in particular, but, I recommend you to
Implement click fraud detection software: There are several click fraud detection software, maybe you used them, maybe you did not, you did not list, all the software you have utilized
Use CAPTCHA: Implementing CAPTCHA's on your website or landing pages can help to prevent bots from clicking on ads.
Limit ad exposure: Consider limiting the geographic areas and devices where your ads are displayed. This can help to reduce the number of potential targets for ad clicking bots.
And finally, note that there is no foolproof solution to prevent ad clicking bots entirely!