Item not delivered with in time

I purchased Hitachi518WEA 1.5 ton AC from Great Eastern Appliances pvt ltd Branch shop 2 Green view 27/1 BT Road Kol 58 on 12/04/2016 and according to the bill the the date of delivery 15/04/2016. But till to day 29/04/2016 they are not giving proper assurances of delivery. I now become shuttle corck and finding me in a state in the hands of sales man and the manager. I severally did phone call to them but their indifferent attitude make harras to me.
If they were not in a position to delivered with in 15/04/2016 so why they wrote the date on the purchased bill? Is it customer service? Everyone should thinks twice for purchase any commodities from Great Eastern Appliances Pvt Ltd.