I feel like the goal for this kind of thing should be to tie up cold callers for as long as possible, so they aren’t bothering others. Ideally you should set it up completely seriously with increasingly apologetic and sincere we value your call hold messages. You want to keep assholes on the hook for as long as possible - so you’d need to break it up with progressive queue length indicators that make it seem like they’re making progress.

I feel like the comedy gold would be to set it up to record the people who think they’re on hold. I mean it would take a lot of filtering or searching - but imagine the people losing their minds waiting on hold forever. Maybe have a sorry you’ve called outside of business hours trap at the end of 10 hours of hold messages and queue progress when they’re at number 2 in the queue, with a voicemail box.