Its actually designed that way. A single order will spawn a number of associated tasks which have to be completed in a specific order. For example, there is no point in trying to configure a BT Vision account, if the actual bearer has not been commissioned.
Some of these task will be issued to other parts of BT, and as each one is completed, the next task in the chain can be issues.
If one of these tasks are delayed for any reason, then things can grind to a halt.
Orders that do not involve other parts of BT, can usually be completed within 48 hours.
You could imagine what chaos would occur if multiple orders were progressed together. Even an order for BT Mobile may be dependent on other parts of BT.
People who place an order, and then decide to cancel, can find that they have to wait a long time before a new order can be placed, with BT or any other provider.
