Phone replacement

Please help,

I bought a Hisense Cell phone on the 12th of July 2019, Now the new phone is very slow and it sometimes stuck today I decided to return a phone and get a replacement but The Stellenbosch Manager told me I need to come with Proof, I mean where am I suppose to find proof as the phone doesn't give me time and place when its about to give me problems, What if it stuck at home at night how must I show her proof, The 7 Days isn't over yet please help as I am not happy with them and the phone as well. I was not impressed with her attitude and the treated I got as a customer, Please give her some training on how to talk with Customers.

Thanks

Pelokazi Mlonyeni Mantshantsha ***