Each flat would normally have it's own cable to the street cabinet. If that hasn't been disconnected at the street, signals may still pass through. However without a paid for service, the signal cannot be decrypted, unless some underhand theft system is being used. We do not discuss the ins and outs of how to do this on here as we do not wish to aid and abet such theft.
As each flat would have been designed for it's own service then you shouldn't be directly affected. However you might want to consider shopping your neighbour :
http://www.cableforum.co.uk/board/10...ous-dodgy.html