Unresolved issue with iStore

I took my phone for a screen repair and battery replacement late November 2019 and my phone was returned on the 4th January 2020. On the 3rd March 2020 I took my phone to iStore with the problem of battery failure, something that I never experienced prior to replacing the battery. The phone was booked in and returned on the 10 March 2020. Throughout lockdown I had a challenge with the phone and I could not understand why because the battery was replaced. I returned the phone to iStore on the 7 September 2020 and I was told that I was not going to pay any cost because the phone was booked for the same reason that I book for in March 2020. To my surprise I got the quotation from iStore technical center on the 9th September 2020 stating that I need to pay more that R8000 for the replacement of my phone. The lady who was handling my phone said the phone is damaged and when I asked what is the problem she did not give me a clear answer. I tried to send my complaint to iStore and the Technical center and no one bothered to assist me.