Trying to pair child’s Apple Watch to my phone which has e-sim

I have an e-SIM with Tello on my Apple phone (as the physical SIM is in use with my old UK number). I got my son an Apple Watch in the summer, paired it with my phone and got a Verizon device plan for him. Since day one I have never been able to successfully call him and texts often take ages or don’t sent at all. He could call me most of the time. Recently nothing is working so we ended up resetting the phone and repairing it several times. I went into the Apple shop and they said it was a Verizon issue. Verizon said it won’t work because I’m not on Verizon? I’m at a loss. I can’t switch to Verizon as I need an e-sim and use my English sim for various things. What can I do? The watch is basically useless and we need it working. As Tello is T-mobile could I switch him to that or does it not work like that?