[jamest101]

they refuse to do anything as GPS shows delivery

GPS only confirms delivery to an "address" and not to a "person", hence you didn't "personally" receive It.

What was their last/recent response?

They have determine the parcel was. Delivered and  they are not responsible for  theft .

Only way that is true is if they either delivered it to you in hand and got a valid signature/OTP code or if they left it in a safe space you specifically stated on delivery option. Otherwise them, or the couriers, are liable.