I need a landline and broadband installed for new home but address not serviceable

I am trying to get a landline and broadband service for my daughter's new home but customer services have said her address isn't serviceable even though the postcode checker says 1Gb service is in the area. Most of the houses on her road are already on the drop down list but not her house. I know her house is about 30m from the road going round the estate but her home backs onto the main road with a different post code and the dwellings/homes which are part of the same building have their front doors on that road (in that post code) why cant a connection made to the rear of my daughter's new home?    Please see attached photo below.