Have you got conveyancers or lawyers doing the settlement on your behalf?
My understanding is that sometimes in the Contract of Sale the vendor may be able to delay the settlement 14 days without any penalties occurring. However I am not sure what action you can take about no new date being proposed.
My suggestion would be to get in contact with a licensed conveyancer or a lawyer. They should be able to assist you practically and legally with your options in this situation.
I have attached an article with your rights as a buyer. Therese is right - the vendor if they give an adequate reason are able to postpone settlement for up to 14 days without penalty.