I bought a pre_owned...

I bought a pre_owned phone from them n a day later from using it, it gave me battery problems and then I took it back 6 days later... So now my problem is since I've took it back on the 16th of March till today I've never received any feedback from them. So today I called and they were just dropping my calls and telling me that i have to wait for 21 days to pass first before I could put out the complain.