But we can limit users using them. For Example whoever has more than 25000 SP wont be allowed to use voting bots in the future

There is no way to prevent users and stakeholders from doing this.

There is another solution which might be even better! Push all promoted posts to the "Promoted" page, whether they use Steemit or voting bots to promote their posts. This method will clean the trending page forever!

Trending is currently based on the amount of upvotes (measured in SP) a post receives. If a post receives sufficient upvotes, it will be in trending. Trending will be replaced once communities are implemented BTW.

So if we will have a live chat to report the problem at the same time and resend the money back to the users or to the reward pool, it will make a big change.

There is already a steemitabuse channel in steem.chat and Discord. There is no way to 'send money back' if it is stolen.

Maybe the scammers accounts should be suspended as well.

This is not possible. I appreciate you are trying to make helpful suggestions, but you should really spend more time to understand how the platform actually works.

My suggestion is to limit the usage of selfupvotes maybe to 10 per day. The most of them dont even read or upvote other users posts, but upvote only their comments.

If this were implemented, the abusers would just create a second account and do all their "self-upvoting" by upvoting account A from account B.