I would inform the buyer that you are going to the police if they do not either cancel the chargeback if they initiated it or reimburse you for the cost of the item plus any charges you get through Paypal if they did in fact use a card they were not authorised to use.

Some banks allow chargebacks up to a year or more while some only give 3 months which is why you should keep all proofs of postage, tracking numbers etc for at least a year.