Multifunction phone

I bought a phone on tuesday 24 August and on Wednesday the phone multifunction on deal pad and also its a dual sim another sim doesn't operate mobile data, so within 7 days we returned the phone to the shop so the manager of the store didnt want us to return the phone she said what must shop do with this cellphone because we bought it. We explained her that but it doesn't satisfy us and she responded that she wont take the phone back so we tried negotiating with her that okay lets add another amount on it take another one she refused also so we need help bow to report this person