I hope your payable order was for the right amount. I sent in my first HO60 claiming £53.54 a few months ago. In due course I got a payable order back for £50.90. There was no explanation of why it was less than I claimed. I might have made a mistake, but the calculation is not that complicated. It is not worth the effort of chasing it for that amount but I hope HMRC are not doing it to everyone and pocketing the difference!