Wrong info to Upgrade

Good day, I have just been phoned by cell c to do an upgrade on one of my contract. According to me the one they phoned me about is due for an upgrade in September 2018. I phoned them back and ask if they can check for me if this is correct to do the upgrade on 4 June 2018 and the lady said no. Can someone please let me know what is the correct date.

Thanks