Upgrade incorrectly done and now I have to pay for his mistake

I m not lucky with MTN, first it was an issue with the loan phone ......now it a mistake done by a consultant on my upgrade......he did a mistake and upgraded a wrong number......now I'm sitting with a bill of two phones and he told me there is nothing he can do as it has passed 7 days of return

I was paying R377 now I will hv to pay R956 for a mistake that was done by the consultant at the MTN branch North cape mall