Any way to cap after reaching transfer limit to prevent high bandwidth bills?

I stubbled several topics here in the community where users had ridiculous high traffics reported for their cheap 5$ VPS. Amounts like 100$ and 250$ for using excess of data.

I started to search, if there is an option to cut off or limit my VPS bandwidth as soon as my monthly datalimit is reached but could not find this.

Because I know that my VPS should never have a high bandwidth as I manage a server for IoT devices for multiple companies. What are my options to cap my bandwidth as soon as I hit the limit for Ubuntu Server?

I do best practices with security, but still I can never be sure if someone some day highjack my server and consuming hundreds of dollars of bandwidth.

I do found (and enabled) the option to get a email notify as soon as there is a lot of out-bound bandwidth transferred but I do notice that this might be to late when I read the email notify and be able to take action to such a notify.

Someone else in a topic was recommending OVH cloud as they automatically cap your bandwidth to 10mpbs as soon as you reach the limit until you take action to buy more space. As I am already comfortable (and happy) with digital ocean, I do not prefer that route. I hope for a option with digital ocean or a software solution inside my Ubuntu server.