A faulty oven was delivered to us and we asked for refund and collection.
The (Non jewish) vendors have arranged for this but they have scheduled it for Chol Hamoed.
Is it permitted to allow for the collection to take place from our home or does it need to be postponed.
It would have been permissible for them to come pick up the faulty oven. This does not constitute making a purchase or sale, they are just picking up what is in effect theirs. If they are replacing it with a working oven which will be used on Chol Hamoed this would be another reason to permit this as a tzorech moed.