Letter for my sim card that has no usage

I wanted to blacklist my cell c number because my phone was ****** and the consultant at cell c told me that i can't blacklist it because it does not have usage and i have to claim for my cellphone insurance. My insurance asked for a letter from cell c that states that i cannot blacklist my cell c sim card so that they can proceed with my claim and when i go to cell c store they told me that they do not give letters of such incidents. Please help me because i need to get a new phone from my insurance and that can only happen if i get a letter from cell c.