Hey Petra. This has been very common with the AG Chrome Selfie. It is believed to be a bug in its 'Android system recovery partition' files - being a manufacturer's fault. Your best bet at the moment is to contact AG Mobile directly by phoning 0861 24 33 33. Tell them you are trying to reset the phone from the 'Android recovery menu' and that you do not get the 'Yes--- delete all user data' option. This is their fault and the service should be free. And it must be a widely known issue to them by now. You can also contact them from their Facebook page here https://www.facebook.com/agcellular