It was a long time ago. I was advertising on Adwords and my ad was getting hit every few seconds. Whomever it was would go to the linked page from the ad and hit a few more pages within just a few seconds and then leave without spending enough time to even see those pages. The clicks were coming from more than just one IP address but it was same thing from all of them.

I suspected it was a competitor paying some bogus group or bot network to run up my clicks and asked Google to look into it. They asked for my log files, which I sent them, but then told me "no problem found".

It cost me several thousand dollars before I realized what was going on. I shut the ad down for a few months and then turned it back on but the same thing happened again right away. I tried again to get them to look into it but got the same response. I refused to pay for those ads and they buried my site in their rankings afterwards.

Not op but Google has been known to ban accounts, even well established ones, for either stupid reasons(like an expired payment method) or unknown reasons, and there's very little you can do about it - other then make a HN post and hope some Google engineers can talk to the right people.