They refusing to exchange a phone that is giving me problems

I went to the store to exchange a phone that I had purchased, and the manager that was helping me said she first wants to see if what I'm telling her is true. I then asked her how will you achieve that when you not using the phone? She then went on saying it's procedure that when I was purchasing they did not tell me about, the only procedure was that within 7 days if I experience any problems I can bring it back with package and slip. The lady took my phone, it's been an hour since I've went to the store. I don't know what to do because now I'm without a phone