Customer asking to cancel the order without prior notice

You can do the following:
1. Trace the phone records you have;
2. File a legal notice to him;
3. Say that you and your customer are bound by a legal contract even if it is oral;
4. Ask for compensation from your customer for the loss you suffered.

you was ordered by customer for computer hardware material, and now he denies to accept. As a rule if a buyer refuses delivery without grounds then they are liable for any subsequent costs incurred by the seller, including reasonable costs

Without any advance it was not supposed to book the order. If you had & customer cancelled you may only request him to receive it else send him legal notice. Remaining i fear that legal costs will be more as compared to your product.