A seller does not have to accept a cancellation request.
Wait until one day after the item's last estimated date for delivery, and open a case for item not received.
Be aware, your seller may send you the item , that is, if you have paid for it, have you?
If it's not paid for, they can cancel the order after 4 days for a non payment, and you'll receive a non payment strike on your account. If you receive another, then you'll not be able to buy from the majority of sellers, for a full 12 months.
@daviemcguire