incorrect on automated invoicing

Hi,

We have been manually invoicing through whmcs for 18 months and about to start making use of the automated invoicing. We invoice with monthly subscriptions (billed in advance) and also other charges from the previous month (billed in arrears), but these need to be included on the same invoice. For example:

Next Month's rental of XYZ Telephone Line: £12.50 (01/05/2014 - 31/05/2014)
Next Month's rental of XYZ Broadband: £25.00 (01/05/2014 - 31/05/2014)
Next Month's rental of XYZ Web Hosting: £6.50 (01/05/2014 - 31/05/2014)
Previous Month's Calls from XYZ Telephone Line: £4.47 (01/04/2014 - 30/04/2014)

By building these products and testing manually with cron, I am generating a separate invoice for the 'Previous Month' line item, whereas I need these to be on the same invoice.

Alternatively, I can cope with losing (DD/MM/YYYY - DD/MM/YYYY) altogether.

Thank you for your help.