Add month number to HMRC reference for export to Telleroo

When the HMRC payment is exported to Telleroo it uses the Accounts Office Reference as the payment reference. This is causing problems with HMRC allocating payments as they expect the AOR followed by the last 2 digits of the tax year followed by the month as a 2 digit number. Payments are sitting unallocated on the customer account and customers are receiving letters from HMRC stating they are overdue with their payment and attracting daily interest charges.