Sometimes, when you're shipping something with your courier, something can happen to change the shipping situation even after you've already sent out the package. While most companies are going to take all the steps possible to make sure this doesn't happen, it's simply impossible to anticipate everything. So, if your fulfillment company has already left with your package in the back of one of their vehicles, is there a way to stop the delivery from being completed.
This is an almost unequivocal yes. In the past, this was much more difficult than it is now. Couriers are now in possession of all of the latest communication technology. This means that you have several different methods by which you can easily communicate with your courier, and they have even more methods by which they can quickly get a message to the driver that is actually carrying the package that needs to be stopped.
When something is being shipped already and you've decided to stop the shipment, the first thing that you need to do is let your courier know to put a stop on the order. Every courier will have a different way that they prefer you to let them know about this. Some will want you to call them, others will prefer an email, and others will have software where you can directly mark on the package in question that you need to stop the order.
Then, the courier will contact the driver and tell them to not deliver the package. They are in constant communication with all drivers through phone calls, email, text messages, and GPS route updates. They will contact them via as many methods as is required until they receive confirmation that the driver has received the instructions and will not carry out the delivery.
This can be a useful tool for you if you need to cancel a delivery quickly, such as because you realized that you shipped the wrong parcel. However, you need to be aware of the consequences that exist should you choose to do this. You're going to face fees from the courier company if you cancel an order while its already on the road. You're basically going to end up paying for shipping to delivery to its destination, and then paying again to ship it back to you. So, just be sure that it is worth it before you notify a courier to put a stop on an order.