Phone issues Premio S86

So I went to the Ackerman's in horizon and the cashier told me that in order for me to get my phone fixed have to go to where I bought the phone. I really don't understand because this is the closest for me as I work near and I'm having issues with he Premio I got in October as the phone's battery is always flat, the apps stop working all the time and when people call, the answer option comes through late or the people drop. Can I please get some assistance as I use this phone for work and business. The speaker is not working if I have to talk to people I have to use earphones