my apple cellular doesn't work when my phone is left at home

I bought the expensive apple cellular 7se and am paying my service provider extra to have cellular on my watch. however every time I leave my cell phone at home the watch can't make calls and says calls failed. and I am in a strong cellular coverage area...its the same places I can use my iPhone and if the iPhone works in this city shouldn't my watch work in this same city?

super frustrating as I thought I could rely on just having the watch with me (and still be able to receive and make calls) and leaving my cellphone at home. why is this not working????????