No consistency with billing

I am a freelancer. Every month I eagerly await my cell phone bill from Vodacom so I can claim back my work phone call expenses, but the date I receive my emailed statements seems to change from month to month, making claiming back these expenses very difficult.

Over the last few months the statements arrived on these days: 8 September 2017 10 October 2017 13 November 2017 8 December 2017 12 January 2018 It's now 18th February 2018, and no sign of any statements...

Once upon a time I was able to access my itemised billing online at any time in the month, but that service was removed a few years ago. Would be nice if they could just get this one simple thing right and send out statements consistently at the same time every month!