hmmmhmmhm parent
If you make such request, how can you enforce to get all of the comms? I'm curious, would some government institution step in and audit their mail servers, slack channels, google hangouts and all other channels to obtain all of the information?
The next stage of complaint is actually the local Information Commissioner.
Companies will usually comply with this, because it's very difficult to instruct staff to not comply with the law without leaving any records or risking one of them leaking it. However they will check what the legal minimum is and do that.
I take it you are unfamiliar with the legal process of "discovery" https://en.wikipedia.org/wiki/Discovery_(law)