Faulty cellphone Hisense U962 at truworths mall of africa

On the 2nd of March 2019 i bought a cellphone U962 for my younger sister at truworths mall of africa. On Wednesday 6 march my younger sister phoned me saying the new cellphone when she charge it , it says battery full but when she remove the cellphone from the charger it says battery is 20% or battery is empty since i was not working around gauteng i told her to bring the cellphone on Saturday 9 march to return it back to truworths. Indeed on Saturday 9 march 2019 i manage to return it at truworths unfortunately they said 7 days is already passed so they can't give me a new phone so they will take the cellphone for repair at mtn and they said it will takes 3 weeks for repair. I went to truworths on 06 April 2019 they said the phone is not yet back from the repair and i was not the only one who has the problem with this cellphone. Most people they report the same fault of battery but still the cellphone is on the shelve, please help me to get my phone because the reason i bought that cellphone is because my sister's phone is broken then now she dnt have a phone. I have been waiting for their call even today no communication or phone call to update me.