Jet campus square

I bought a Nokia c20 at Jet campus square. The phone has been giving me issues but could not return on time coz I was not feeling well so got my strength back and could only return it 2 days after the 7 days have passed. I tried taking the phone back today but was denied to exchange the phone. My job requires that I navigate a lot coz sometimes I go to places I'm not fami**** with and this phone doesn't even navigate, the network work is bad but when I put my sim on my friends phone the network is great, I can't answer some of my calls coz when it rings it doesn't show the answering screen or delays the answer screen. Was told the only option I have is to have it checked out and it will take 26 days can't stay 26 days with out a phone can't even stay a day without a phone coz I need to for work.