It seems they have already shut down the service voluntarily today, citing law enforcement measures towards them. See the announcement on https://exch.cx:

I had tried to access their new main domain (exch.net) earlier and got an error. In light of the announcement, it is likely that this domain was taken down, leaving only exch.cx and the onion domains active.

Best wishes for the exch team and R.I.P. to an excellent service.