I have the same issue with my Stylo4.
The difference being that your motog7 is still supported.
What support told me is that if your new phone is replacing your old one, it can't be re used for a new line.
Makes no sense, but that's their policy i guess.
I've chatted online and talked over the phone on numerous occasions to get my previous phone (stylo4) added as a new line with a new number. 6 out of 7 said they can do it and to wait 20 minutes, nothing happened. 1 told me they can't do it since it's a replacement phone.
Based on my experience, you're better off buying another new phone if you're looking to get a second or third line.
For the record, the online chat and phone call disconnected me mid conversation and put me in a waiting list estimated at over an hour waiting time.
I hope you're able to get yours to work.
Just letting you know my experience.