One specific number is being forwarded

I recently ported over our former landline number to a cell

phone for my son. (We’re all using iPhones.) Initially I had problems calling my son’s new number - I don’t really know why but it resolved after I deleted the number from my Contact card and my contact info. So now I can call his iPhone. But when my husband tries from his iPhone, the calls forward to my number. Even when we physically type in my son’s phone number. My husband has gone through his phone and we can’t figure out where the hiccup is…the number must still be associated with me, and I think it’s an issue with the iPhone and not a carrier issue. Anyone have any ideas? My husband can text our son’s number fine…but in an emergency, etc., he needs to be able to actually call the phone number. Call forwarding is off on all phones. I’ve shut them down and restarted them several times. I appreciate any suggestions.