Number Sync on iPad

I have followed these instructions and I annoy getting number sync to work on my LTE iPad mini 4 

https://www.att.com/support/article/wireless/KM1062368/

I can make and receive calls when both phone and iPad are on WiFi but not when the iPad is not on WiFi with phone... this is supposed to work like the LTE Apple Watch (it worked for me when I was on Verizon)

i went into MyATT app and noticed that when I tap on the iPad under services and option numbersync is not listed  like it is on my Apple Watch...

what else can can I do?