Norton 360 and NOBU - old PCs and ghost storage

Hi. I have 6 computers on Norton 360 subscriptions, all of which backup locally to a shared location. I am happy with this, but now need a new online backup solution as my current one is finishing. After much research I am trialing Norton Online Backup as it fits my situation and seems to add to my current online 360 storage space. On setting up the NOBU I see that there are some of my old computers (and 1 of the current computers) shown as using online space. Strange as I cant remember setting any of them to do this, and I cant find any way to delete these old computers from the account, none of them are available any more, having died over time. When I look at the 360 on the listed current computer it is not showing an online backup set only the local one. Does anyone know if there is a way to free up this space and remove these computers from the account? Thanks. indecision