Upgrade nightmare

I have had my current phone since 2014 and now it has started giving me problems and I realized its time for a new cell phone device. And since I have an existing contract with Cell C and due for an upgrade, I upgraded on the 26th of June 2018. I was expecting my new phone to be delivered the next day or the day after but there was no update from Cell C. Mind you my phone switches off even when my battery is 90% charged. So today I decided to make an enquiry as to when will they deliver my phone? Now they are telling me they are out of stock and the agent that I dealt with should have informed me of this, but she did not. I feel like Cell C has wasted my time and made it worse by being dishonest when they knew they had no stock and failed to inform me as their customer. They were suppose to inform me so that I decide whether to opt for another provider as I am now missing very important calls as my phone needs to be in a charger always or it switches off. Can someone correct this and Cell C deliver my phone to me please.