NEED HELP!

Good day po! Ask ko lang wats d best way to solve my prob. Nag purchase kc ako ng phone from an online seller pro same location kng kami here in davao po. We actually met each oder by the time na kinuha ko na yung inorder ko sa knya. Sa bahay pa talaga nila. After 3days po ngka prob yung unit so i informed the seller nd sabi nya ibalik ko daw sa knya for replacement kc under warranty pa nd replacement. I returned d phone by saturday nd HE promised to give me a new unit by wednesday. Den wednesday came nd wla cyang nabigay kc ganito ganyan. I consider nman he's reason kung bkit wla pa so he promised again to give me the unit on saturday dat week pro wla prin. Kesyo gnito gnyan raw. He promised again na sa monday daw nd he will personally deliver it in our house pro wla prin until now. Its been 2weeks na nd wla prin ung unit. I NEED SOME ADVICE ON WHAT TO DO w/ THIS MATTER. Please! btw, dis morning lng nag promise ulit cya na ideliver nya later around 2pm.