The first thing is, do not panic! Most likely this issue can be resolved by setting Homey into recovery. Follow the steps in this article to set Homey into recovery mode.
Is Homey still acting up? Then we need some professional help in solving this issue for you! Please contact support via this form. Make sure to include the original invoice of your Homey, this will speed up the proces of fixing this issue for you.
Note: a Diagnostics Report is not necessary in this case, you can just fill out "not applicable" in the Diagnostics Report field.