I can't make a comment on other posts due to less than 50 reputation, so I'll put my thoughts here.
Regarding the testing comment from Andrew Martin, you could use it as a hypothetical scenario to see how the user judges the question and see what response is given. I do agree that it is a negative scenario though and that this could provoke a negative response from the user, and potentially make them less willing to provide information. You could end the user interview with this question to not tamper with other results.
In terms of communication, it would be determined by the user's communication preferences they setup when creating an account. It also would be decided by your companies policy on communicating changes to a user's account. I know PayPal e-mail you any changes to your account, whether it is a suspension, permanent bans or even privacy changes. The e-mail method will allow more information to be provided and give the user links to be able to appeal bans or check the status of their appeals and it is more professional. SMS/Whatsapp comes across as too personal for a negative impact to the user. You could prompt the user via SMS/Whatsapp to check their email, but it would depend on how you message this across.
Hope this helps. Keep us updated as I'd like to know the outcome :)