Unhappy customer

Ackermans 1228 Soshanguve crossing shop,02/08/2021 I made a phone lay-by nokia C10 but I didn't exactly want Nokia C10 the one I wanted it wasn't there,I thought am going to change it wen my lay-by is done.ok on the de my lay-by was done I explained the cashier that I didn't want that phone am requesting to change to the one I want because that day it was there,the cashier refuses me to change it now the phone is giving me a network problem and they didn't explain me About that phone.the network is very slow so I want them to change that phone for me to the one I wanted.thanks