I've had my FireTV Cube for about 6-8 months. The past 2 months, it has started freezing and the only way to get back is to unplug the power. I worked with someone from Amazon on chat, and I believe they had me unregister then re-register the device. It still is having issues, and they happen about every 1-2 weeks now. My wife got so frustrated with it that I moved my Roku Ultra downstairs and replaced the Cube with it until I can either get it working right again or if I can get a replacement.
If you have already been in contact with our Customer Service but the problem is still unresolved, I suggest you to recontact us and ask for a replacement of your device as long as it is under warranty.