In the US at least, you can serve debt collectors notice that they must cease all future communications with you, and if they disregard that, the FTC can and will go after them.

I'd recommend reading the Fair Debt Collection Practices Act.

https://www.ftc.gov/enforcement/rules/rulemaking-regulatory-...

I hate debt collectors as much as anyone, but they do have quite a few rules. Most jurisdictions have times during which you can call someone (collects need to be sure to adjust for the destination timezone; since they might not realize they're called at 6am if they're on a different coast).

In Australia (if they show Tricky Business is at all realistic), Mercantile agents can't present you with a notice in front of other people and must serve you in person (similar to a legal summons in the US).

So there are _some_ regulations in place.