Series 4 watch Can not send/receive SMS while on cellular with iPhone 6S turned on

I have an iPhone 6S paired to an Apple Watch Series 4. However, when the Apple watch is not connected to the phone via bluetooth, it will note receive or send SMS or iMessages sent to my phone number. It continues to receive iMessages if they send directly to my apple id. I've unpaired and repaired, reset the network settings, logged out of iMessages and back in on all devices, and Apple support has replaced the apple watch. All of which has not resolved the issue. Apple support says they have no further suggestions. Has anyone else experienced this and have any other solutions? Could it be a bug in my phone software from the years of use?