Will connect to addons via 4G but not WiFi

Hi All,
I have installed Kodi 17 on my phone, PC and got it on an Android Box. I want to primarily use my Android TV Box but can’t get it to do anything. It seems to work fine when I connect it via my phone hotspot but it will not connect to any server or addon (kodi or not) using my home WIFI. The other apps on the box work fine (Youtube etc) and it indicates it is connected. My ISP advise they have no ‘home shield’ on their service and they were unable to solve the problem over the phone. I know the issue is with my ISP/Router but can’t find anything on Youtube or Google that seems to help. I have been working on this for a week now and it’s driving me mad. Please anyone help!