I have an issue where I cannot send or receive text messages with an iPhone user (my father). This issue first surfaced a year or so ago on my previous device (HTC Droid DNA) and has persisted with my new device (Samsung Galaxy S7), so it does not appear to be a device-specific issue. I can successfully send and receive text messages with other iPhone users. Both of us are Verizon customers. When I try to send my father a text message it appears to go through, but when I check the status later it just says "Failed"; clicking on "Message Info" just tells me "Failed".
I tried de-registering my number from iMessage but was informed that my number was not registered with iMessage (which makes sense given that I've never owned an iPhone). I have no idea what the problem could be as this appears to be the only person I have this issue with.