Reporting part-time earnings while on benefits - 18 weeks in

My hours change every week at my new part-time job and I am afraid of reporting wrongly. I have been trying to stay organised about it. Pay posts on a different day from when I work. Who can I ask without risking my claim?

I estimated and then checked my pay stub. When there was a small difference I wrote to the agency to correct it.

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