I would say to try these ideas (assuming you're using your phone or tablet):
Push the camera button to get inside the tank and see if you still have a problem
Completely shut down your phone/tablet, let it sit for at least 30 seconds, then reboot.
Delete and then re-install the game.
If none of that works, then contact This email address is being protected from spambots. You need JavaScript enabled to view it.. Provide them with full details as to what device you're using