No Infrastructure or Wiring at House, but "Previous Account" Stopping My Install?

I bought a house on 11th August 2025, and recently ordered M350 Full Fibre with an engineer install date of 11th October 2025. However, I have since been contacted to say that there is a previous account registered at the address and therefore my install cannot continue. The sales team tell me they will try to contact the previous owners to get the account cancelled, but I think an error has been made. There is no Virgin installation or infrastructure of any kind, anywhere, on the property. No omnibox, no cabling, no old trunking, absolutely nothing. There is a BT Master socket and overhead (copper) wire, but nothing else. I cannot see how the previous owners could have had a Virgin account without any installation hardware at the propery. I am also concerned that if the install does go ahead on 11th October (which seems unlikely), the engineer will be expecting the basis infrastructure to be in  place already - which clearly it isn't.

I tried phoning the pre-install team for further advice, but they were unable to help while the sales team are chasing down the previous account holders - which to the best of my knowledge, do not exist.