Hi!
Where to complain? I bought my Iphone in second hand, I believe a lot of users did the same, we don't know if the equipments were modified, and till which extension.
I've heard that with this new IOS 11, seems that changes like touchscreen, and other components can compromise de activation, I hope that's just nonsense.
I manage to schedule a support call, which I wasted a morning waiting for the call plus the procedure of downloading and installing the new IOS 11.1.2, plus waiting for the support to call me again. And in the end nothing solved, and I was redirected to a support center that represents Apple (which I will not go, because it was working before the update, it's not an hardware fault)