New Cell Phone giving me problems

I bought a new Samsung J1 Ace at Sport Scene The Grove mall on Tuesday the 3rd. the next day while trying to setup my phone i realised that it had nertowokr problems and it couldnt stay connected to the internet and the Vodacom nertwork i took it in for service at Vodacom Customer Care Menlyn they noticed the problem and booked it in for repairs on Sunday the 8th they sent me a massage the same day that i can collect my phone, i collected it on Mondat the 9th they told me that if it gives me the same problem i must return it to the storewhere i bought it and they will give me a new phone. on tuesday the 10th my phone started again this time saying \no service"i took it to SportScene The Grove Mall and the sales lady who sold me the phone told me that if they take the phone i will be charged for brining in the phonewhile there was nothin wrong with the phone and that i should keep the phone for 2weeks before booking it in because she wont take the phone back... the phone still has 7days warranty. the phone is still not working now and still gives \""no Service\"" massage. i am unhappy with this service. what must i now do with this phone? """