I need to inform someone that all further communication needs to be via the email address they have for me. This is due to me changing my phone number and frankly I dont trust them not to pass on my new phone number either deliberately or accidentally to a certain person. Unfortunately I have to make it known the phone number they have for me is no longer valid so I can't just dodge it as a request to switch to email in future.
How do I word this without sounding rude/accusing/etc?