I'm glad your mum was able to help you use some skills.
Can I ask this? You don't have to respond. I'm just wondering if you see the difference between believing whether or not the voices are telling the truth, and believing whether or not they exist?
Like, can you acknowledge that they are very real for you, but also that they might be lying? Or are those things tied together? Would disbelieving them somehow make them less real? (Either to you or based on what they say, since those can also differ)