A3 and SQ have an interline agreement. However, interline agreements are irrelevant when it comes to separate bookings, where it is down to the informal option for an agent to do so. I doubt it has anything to do with Covid, so I would not expect you to be able to check through to CFU, but you may get a sympathetic agent who can do this for you. There is no point calling anyone, since the decision will be taken on the day.