How do you get staff to actually use AI tools instead of ignoring them?

We rolled out an AI document drafting tool six months ago. Licence costs are £4k/month. Actual monthly active users: 12 out of 80. The 12 who use it love it. The 68 who don't have various reasons — too busy to learn, don't trust the output, "I tried it once and it was wrong." We've done two training sessions. What does effective AI change management actually look like at a professional services firm where the culture is cautious and the staff are time-poor?