Unethj, displeasing service

So I joined the company back in 2018 when I bought a new device with MTN, fast forward 2021 I loose the device in December and make a claim for it, mind you I have been paying my monthly fees with no hestitaion, my claim was responded a month later even so it was declined the reason for the claim being denied is invalid as well. I went again and appealed the claim and declared it false and corrected the mistake till this day my emails are not being responded furthermore the consultants as well as the company have been unethical in so many ways. It is disappointing to know that I have been paying on time, my claim is as per agreed on the contract however still being denied and the service I'm getting highly disappointing to. I need help with the resolution to this matter!