Bad service from telkom

Can anyone advise me what to do regarding a problem I have with Telkom..

My contract with telkom was due for an upgrade and I did the upgrade yesterday (15th). On the same day while I was setting up the phone and registering my fingerprint on the device I noticed that the phone freeze and restarts. I thought nothing of it at the time and just left it. However, the phone is still restarting on its own without me doing anything on it. I took the phone back to the store today and the sales agent that assisted me yesterday, assisted me again today. She told me that I have to book the phone in and they will let me know in 10 days and have it looked it. They will then decide to have it either fixed or replaced. I've told the lady "I can't book it in , as I need it for work purposes and I've had it just for a couple of hours, how can you tell me to book it in". She then reset the phone and told me to bring it back before the 7 day out of box warranty ends....the same problem happened again afterwards, Twice!! . On top of that both my telkom, MTN and wifi has an unstable connection whereby it disconnects all at once. All I want is them to replace this device with a new one and booking it in due to this problem is an inconvenience.

Any advice on how to deal with this? As I can't sit without a phone for work purposes.