The facts of this case are not entirely clear to me, but on the general principle of re-visiting previous decisions, this is usually covered by the Council’s standing orders. For example the NALC model standing orders say: ‘A resolution shall not be reversed within six months except either by a special motion, which requires written notice by at least 2 councillors … or by a motion moved in pursuance of the recommendation of a committee or a sub-committee. ‘
I don’t understand what a ‘granted decision’ is. Parish Councils do not have planning and development powers, although they have the right to be consulted on some matters by the local planning authority.
Decisions of the Parish Council must be made in open session and seen to be agreed by a majority. If you believe that a decision has been taken on the basis of factually inaccurate information, then I suggest that you would have to take this up with the Chair of the Parish Council, or possibly other Parish Councillors. Also most Parish Councils have an open session for the public to make comments and ask questions.