You can call your product whatever you like, but strictly speaking, it will not be glass-ceramics, but ceramics with a glass phase, since the production technology is ceramic. For example, no one calls porcelain glass-ceramics, although it can contain up to 70% glass.

no

Technically no - glass ceramics can be ceramics crystals with a glassy matrix or glasses that have nucleated an grown into ceramics (think Corningware).

You have a sintered glass