anonythemouse: receipts are not required since payment is not for actual expenditure. The payment is a Flat Rate Expense with entitlement base upon your employment and already negotiated rates. So long as you can show evidence [not hard] that you were entitled for the period you want to claim back, there should be no problem. It may be that the 'technician' you dealt with was not a 'technical' in the subject as required. If so I recommend that you go to the relevant section of the web site and research the procedure then phone the erk and educate him.
See Retrospection
http://www.hmrc.gov.uk/manuals/eimmanual/EIM32725.htm
http://www.hmrc.gov.uk/manuals/eimanual/EIM50057.htm
http://www.hmrc.gov.uk/manuals/eimanual/EIM50058.htm
Best Wishes