Apple Watch and DIGITS

I have digits app on my phone, because I use it to transfer my work phone calls to my cell. I just bought an Apple Watch SE cellular. So I can take the phone calls without carrying my cell phone with me.

When I received phone calls trough the digits app my watch doesn’t ring only my phone.

I called T-mobile 4 times in one day  for someone to help me to fix this problem and was told the Apple watch won’t work with digits app even if it is paid with my phone.

Can you please help me? I talk to T-Force., Customer care,. Digits department. Nobody seems to know the solution. 
 The ad says it work with call and watch even if I don’t have the phone with me.