Having iphone to iphone text(sms) continuity issues

Hey all,

So here's my setup. Have an Iphone 7 (work) and an Iphone 6 (personal) both on the same cellular network (Rogers) and fully updated, both signed in with the same apple ID, and really same settings. 2 different sim cards/phone numbers. Have forwarded calls and sms from the 6 to the 7. Phone forwarding is working fine, but sms is spotty. Am getting all sms sent to either number on both phones, but when I try to reply to a text message sent to the 6 from the 7 I almost always get a message send failure notification. I can't figure out what the issue is, I've deactivated imessage and facetime on both phones and restarted both and that seemed to work for about a day and now it's back to not working again. Anyone experience a similar problem?

Don't want to carry both phones around with me. Also was doing the exact same thing with the Iphone 6 (work) and an Iphone 5 (personal) for over a year, before upgrading the 5 to a 7 and swapping the sim cards...