Both appear to be wrong.
Attic conversions normally require a raised floor to avoid damage to the ceiling below.
6.5 inch joists are substandard depth, which is normally 8 inches depending on the spacing, span and load.
You need to retain a building professional to advise you on such matters - you cannot sue the local authority on provate development like this, but they can take you to court for not building compliantly.
There are other issues you need to be aware of involving insulation, interstitial condensation and venting as well as fire safety and your building professional can advise you of these,
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.