Mmm ... I would have a serious think about changing those couriers if you use them frequently to deliver goods, and they are unable to provide you written confirmation of the address that goods were delivered to.

It leaves you without paypal seller protection, not only for chargebacks, but also for not-received claims.

Just my opinion, take it or leave it, but personally I would get back on the blower to the couriers and be insisting that they provided written confirmation ASAP that the goods were delivered to a particular address - it is the service you paid for and you verification that they provided that service - in detail.