no - at least in WA - they can't stop you closing an account. they usually leave the supply on for 3 or 4 months on the assumption that someone else will probably connect up an account for that address.
as for medical blah blah, it is up to the occupant to notifythe elctric board if they have such a requirement. You are merely closing an account. it is up to the power co to decide whether to cease supply
whenever you offer a service you need to be rewarded for effort and risk. these people are abusing your good nature.
for goodness sake, disconenct the power and let these grown adults look after themselves