I don’t know what State/Territory you’re in but as you’ve referred to an Executive Council I assume that your Plan is in WA (?).
KiwiPaul‘s provided a QLD perspective, and whilst Strata Legislation varies from State to State what’s he’s advised is pretty much spot-on irrespective of where your Plan is located.
Whatever Legislation applies, in my opinion the common principle is that if a Council Member isn’t currently delegated to approve the engagement of Contractors and/or to authorise the payment of their Invoices and they have, and there was no budget allocation for the works involved, then they’re at fault for not first taking the matter of the works on their apartment to the other Members and/or to the Strata Company, and so is the Strata Manager or whoever it was who engaged the Contractor (at fault) by issuing the work order and by drawing the cheque.
You mentioned that a cheque had been made out and that works on the apartment had been stopped, but has the Contractor been paid, part-paid, or not yet paid, and has your Strata as yet assessed whether the works on the apartment are the responsibility of the Strata Company or the apartment Owner?
I and others who may respond further to your post would need to know that in order to more fully advise.