I just went to both of those sites to check. The British Gas site's Chat option says it's not currently working (although this might be because I tried it after hours). The Curry's site only has a video call option, and no chat (and a video call would require you to grant the site permission to access your camera and mic, so make sure you've done that).
If you go to the British Gas chat option when they're open, does it say on Chrome that it's not currently working, but it does work on Tor?