I checked for the papers. I see in the attached time sheet in original:
Travel time: 2* 2,5 h
Working time: 1* 4,0 h
I assume, that you did not charge for the breaking time in your time charge with the invoice? This sheet is not attached to check. But just make sure that it shows the above mentioned times.
Also for further services, I would highly recommend that you would also show up with a breaking time. For general it is not normal “not to need food” during the day. If the engineers are eating while travelling time, that is fine and should be explained somewhere (mail is ok). Could be a point of discussing..
I cross my fingers,
Have a nice evening