If you Ipad has EVER been into a street service and had any part replaced, you wil NEVER be able to activate it again. The moment you updated it from ios 9 to ios 11, you turned it into a brick , as ios 11 doesn't allow anymore for apple devices with replaced parts (or refurbished devices) to activate. Go to that service again and if he can fix this, in ANY way, you're in luck buddy. My IpadMini2 is a brick in my drawer since last year.
If you have an apple device that has been, for whatever hardware issue, sent into a normal service (non official apple), you will never be able to activate your device again if you were unlucky enough to update it to ios 11. Apple stealthly locked all repaired/refurbished devices with ios11.