While I’m not sure why you need written documentation, go to the hub and ask that they close your account. Then if they can’t provide you with something written, take a screenshot showing your account is no longer active.
if you ever need or desire to reactivate yourself you can VS them deactivating you would be more difficult.
I have rideshare insurance. I was told that once I have it on my car if I want to take it off my car in the future because I decide to no longer use my car for rideshare I'd have to show I no longer do it. I asked how the heck I'm supposed to do that and they told me to show the app to them showing my car is no longer available for it.
That makes no sense, because I could just take it off then put it back on, but I guess I'll see what happens down the road.