unhappy service

bought a phone hisense on the 4th of January. phone gave me problems with 3 days (battery not lasting a day and network not stable) . Try to send the phone back within 7 days of purchase. salesperson (Zweli) didn't want to take the phone saying i have too many applications open and my data mobile is on. hence the battery becomes exhausted or doesn't function properly. the persist on giving me problems went back for him to exchange or give my money back. since the phone was reported within 7days. he told me his going to book the phone close to 6 weeks. and i can not have a phone for that long. i dont understand why i cant get my full refund,