I am scheduled to have the Service activation for Broadband tomorrow but it means my broadband will be down for 30 minutes or maybe longer. I am working from home and my son has an online test tomorrow so I need to delay the activation. How do I do this when BT are not contactable by phone
BT are contactable by phone but you've left this until the very last minute. I think you'll be very lucky trying to get it stopped.
Why do you think it will take 30mins or more to do a 2 min job?
If you're transferring from another provider to BT, It's past the point of no return now, I wouldn't even try and change it at this stage.
You run the risk of the cease from the old provider going ahead and the new provide not taking place, you'll end up with no service.
If your son's test is important to not lose a connection, I'd suggest using mobile data if your provider supports tethering.