Question for Consumer Protection Council (imo State Committee)

Please I bought a Techno phone from a dealer here in Owerri. The phone have a guarantee of 12 months and I have used the phone for just 3 months. Recently, the phone developed problem and could not be put on again. I called the dealer and told him and he was like He is not ready to change the phone for me. Please I want to ask if he is not supposed to change the phone for me based on the guarantee? Thank you.