Unfairly billed for a second hand router after my new router was taken by the technician.

I am having countless problems with Capricom. A change over was done at my house in January 2022. The technician came out to do the change over from my previous provider, Communication was absolutely terrible to say the least. The WIFI router was replaced (by a second hand router) by the technician again with no communication and the router was a few months old, still used it with the previous provider with no issues whatsoever). The technician left and took MY router with them. I then got an invoice from Capricom whereby I'm being charged for the second hand replacement router and as previously mentioned my new router was taken by the technician. I took this up with Capricom with numerous mails and receiving absolutely no feedback ever since 04 August 2022.