Cable TV is not IPTV like you get over a phone line. It works on linear broadcast channels the same as Satellite & Terrestrial TV (ie It uses a huge chunk of radio spectrum to deliver all 200+ channels to the box all the time, no matter which ones you are actually watching. Therefore the TiVO needs a coaxial connection which will have to be installed by a technican (as specialised cable is used & signal levels will require adjustment at the street cabinet). The powerline connection is only required if you want to stream recordings to another TiVO on your account, & to use a smartphone or tablet as a remote.
The cost to make the changes (as it is not fault related) will cost £99
The only alternative is to leave the TiVO where it is & install a long HDMI cable.