VOX account

After canceling my fibre subscription with vox I was told they would collect the micortik router supp**** with the installation which I had no problem in doing as I have no use for it, I then called Vox customer support and requested that they make note of the address where to collect the router. I was told the courier will contact me before collecting the hardware I did not receive a call, about 3 months later a received a invoice for the equipment that needs to be paid, after calling Vox customer support again they requested I send the hardware back at my own cost which is obserd as I am not the one at fault, I don't mind sending back the equipment but I should not be liable