Disgusting service

I purchased the Samsung handset but was given the wrong model instead of the one I pointed from the display table.... When I returned the phone the next morning I was told to leave the phone and the purchase slip as the person who holds the cellphones storage keys was coming late in the store. When I returned in the afternoon I was told that the phone cannot be returned back, customer services gave me the area manager(Celeste) contact details whom I contacted to no avail, left the voicemail asking them to call me back but I have been waiting for the call as from Friday. I never skipped a monthly installment but I deserve to be treated like this. I am so livid...