Repeating the above comments also, they only have authority to build using the exact specifications of the approved plans. Minor indiscretions can cause huge problems for the developers but your seems to be a major fault with the construction.
It would be tempting to leave them to build further but then we are being a little bit cynical so in order to get it resolved make sure you a reading the plans correctly and then go along to the council and ask for an inspection of the plans and the progress, which is of course outside of the plans parameters.