MTN bad Cellphone Network

i have bought a hisense cellphone at Mr price Germiston through mtn network then 8 days later i had a network problem and screen was blank i took it back to the shop for repairs which was 25 January 2019 but till today i haven't received my phone when i called i was told it will come back i called every day to ask about the phone but they give empty promises and i fail to understand why should it take that long because i bought the phone because i needed it so now i wasted my money to buy something that i have weeks without, and i was advised by the cellphone consultant the those phones had a problem but re-assured me that they are fixed but its clear that they were not fixed because the phone had a problem within 8 days i am so unhappy with hisense and MTN