Unable to switch phone number

I have 2 active Smarty SIMs and I now wish to change the phone number on one of them, however, when I log onto my dashboard it only records the number of the other phone that I do not wish to change. I now have a PAC number but seem unable to proceed with the switch. Can someone please explain a way forward on this as I also seem unable to work out how to actually speak to someone on the phone or via web-chat. Thanks, Peter.