How do you report hours that vary week to week? (update)

I picked up part-time shifts as a delivery driver and I am confused about how to report them. Pay posts on a different day from when I work. Who can I ask without risking my claim?

The claimant handbook has worked examples for part-time pay. Mine was clearer than the phone line.

Thanks for writing this out. I went through something close to it 5 months ago, and it settled down once I kept a simple log of every call and form.